I apologize in advance, this will be kind of long.
Ok my personal thoughts on this sort of conflict with what the main stream says. The main stream in the glider community in general, scream to get a cage mate immediately. I do not.
I don't do that for several reasons the first is, it's not a realistic expectation of already overwhelmed new owners that barely have a handle on the glider they already have.
I also feel it makes the new owner feel guilty for buying or receiving a single glider, when we shouldn't be making people feel guilty for a decision that is not ours to make.
There is more to it than simply going out and buying a second glider. There are far to many things that are not factored in when buying a second glider because people rush out and get the first one they find to be considered a GOOD new owner by the community they are asking help from.
New owners are quickly in over their head at this point and have very few people willing to spend the time to help them do introductions in a safe manner.
So then we have brand new owners buying a second glider they probably can't afford yet and don't have a second cage and enough supplies built up to house two gliders in separate cages until they can safely be introduced.
Brilliant isn't it? So what happens is, the new owner gets home with new glider and has no where to put it so it goes right into the cage with the current glider. It might work out ok, it might end with one of the gliders dying. Bottom line it's a risk. The new glider may be carrying parasites or an illness that the other glider can get. The gliders may fight, one may be injured then we have vet bills the new owner can't afford. If one of the gliders are injured and need separated and there is no other cage to put the injured one in then what?
All the people screaming GET A CAGE MATE they neeeeeeed a cage mate! They will die without a cage mate they will self mutilate without a cage mate!!!!.... don't ever tell the new owners any of this, just go out and get a cage mate end of story. The new owner is not prepared for this and have no one to guide them through the process cause those same people screaming for you to go get another glider are to busy telling someone else the same thing to help you with the glider you bought because of them.
Myths
1 the glider will die if it doesn't have a cage mate. False
2 the glider will self mutilate if it doesn't have a cage mate. False
3 the glider will be depressed if it doesn't have a cage mate. Sometimes. But there are signs and behaviors that will give you signs that that is the case and it's not always the case at all.
4 the glider won't thrive if it's by itself. Depends on the glider some do some don't.
5 Every glider needs a cage mate. FALSE. Some gliders do not want a cage mate. Some gliders have killed every cage mate they have been introduced to, that is fact and I can produce owners that have dealt with that.
There will be people that will argue and disagree with me on all this and that's ok, but if I ask them for proof they can not produce any. All they can produce is the fact that gliders are colony animals and are known to do better in a colony environment.
Do I think that cage mates can be and are beneficial to most gliders? Yes, in general I do. However, every glider is an individual with individual needs. Some gliders don't need a cage mate. To determine if you should get a cage mate or not get to know the glider you already have. Get to know his "normal" and what it looks like so you will recognize when his behavior is NOT his normal.
If he shows signs, such as over grooming ( and if your not sure what this is or what it looks like please ask I will show you with pics ) If he develops habitual habits like back flips, circles, excessive grooming, running on the wheel more those are signs that a change is needed.
If you feel you will want to add another glider start preparing before you buy the second glider. Get a temp cage, keep in mind the glider should be in the temp cage for about a month possibly longer. Get a second wheel, more toys, extra pouches and accessories, a second bonding bag, water bottle... Buy things here and there so it's not so hard on your wallet. Save up for vet bills, a wellness exam and fecal test on the new glider to ensure it's healthy before introducing it to yours. Prepare in advance will make it much easier rather than scrambling to get what you need after the purchase.
Do I feel there is an age limit to introduce a new glider ? No, I don't, if that is what's best for that glider. Gliders as old as 9 10 11 yrs old that have always been alone have been successfully introduce to new gliders. Again it depends on the glider.
Choosing an appropriate cage mate is also important and many don't do that or don't know how to do that. The last glider I got was given to me. Danzig my adolescent male was paired with her by me telling Bourbon about Danzig about his behaviors and habits about his insecurities and crabbiness. She said Cocoa will be well suited for him. The minute he was introduced to her he became a whole new glider. She exudes confidence, she walked in and owned the cage like it had always been hers. She also acts like I raised her by hand from the first day she got here ( she's about 2 yrs old when she arrived here ) she won't leave my body since she won't leave my body now he won't either he used to not stay on me at all lol. Their dynamic is like nothing I've seen in my other cages and they are amazing to watch.
Now If I had just gone out and bought a glider would this be the case? not likely. If I had bought another insecure glider, I'd have two insecure gliders on my hands, two crabby babies, two gliders jumping off me. It really made a difference having the breeder be involved with who would go well with him. Not all breeders will do this with you though some are just out for the quick sale.
Once you make the choice to get a 2nd. Research different introduction methods and get familiar with more than one method. I have done several different kinds of introductions, some were successful some were not. One ended with injuries to a female. It's a risk no matter how well researched and planned out it is.
Before intro's also get yourself a bottle of Vetericyn VF you can find it on amazon for about 20 bucks. It's amazing stuff that I feel every glider owner should have on hand.
It is safe to spray it anywhere on the glider including the eyes and face, it's safe if they ingest it from grooming as well. It heals scratches and cuts and bite wounds much faster than without it and is a antibacterial that will help keep the wound clean in case you can't get to the vet immediately at least you will have that to apply to the wound at home.
If you get a second cage and a second glider make sure the cages are at least 12 inches apart to prevent tail injuries from the other glider. Tails stick out about 7 o 8 inches a gliders reach with their arm is about 3 inches that's 10 inches right there.... so at least 12 inches apart or have a safe solid divider between the two cages.
Another thing to consider is, Is your male intact or neutered? If he is intact it would be wise to neuter before you introduce to another male and the new male should be neutered as well. If the 2nd is a female they will breed if he is intact and if you don't have his lineage you have no idea if you will be inbreeding or not. This is a whole other long topic and discussion ...
I think I have covered everything except in depth introduction methods, which I can do another post about if you'd like. I would advise you to get to know what is available to you where you are located. Are you thinking about a joey or an older glider in need of a new home? What breeders are local to you, is there a reputable rescue near you ? If you'd like to give me your lactation I can probably give you some recommendations. I know glider folks all over the country and if I don't know someone near you I can find someone near you.