There is a couple who is selling a pair of females, what I’ve been looking for. Though, they have bonded with those people, so, if I buy them from them would it be easier to bond with than a pair of babies and will they like me as much as a baby if I bond with them?

when we got sophie, she was friendly and sweet. She jumped on our shoulder, peed on us (marking us as her property), let us pick her up, pet her and sleep in our shirt.
When we got gus, he was friendly and sweet, loves to be on us, looking for a place to jump and run, lets us pick him up and acts like we have always been his best friend.

So the nice and friendly gliders we got seemed to be just as nice and friendly with us as with first owners, they had a good trust of humans.

Sweet pea, pigpen were shy and slighly scared with first owners, acted the same way with us.

We got link and gizmo as babies, gizmo bonded with my wife in a few months, link was the kids, they let him be, finally I started working with him, after several long months he now likes me, specially for treats, he a fat one.

My two were bonded to their previous owner, and they warmed right up to me. One crawled out of the pouch in the car the day I got them and crawled all over me, and he is the "less friendly" of the two, relatively speaking. I was a bit worried he'd try to hide under the seat or something but nope, he knew from the start that I was the safest spot and his human. They have never had any fear of me and are very interactice, always wanting treats, praise, and to play with me.

If the gliders are well-socialized with humans, they should bond with a new human just fine, and much faster than a rarely-handled baby would. One of mine was younger, only 8 months when I got him and born at the last owner's, and the other was 2, and I am his 3rd home (actually his 4th or possibly more, if you are counting the breeder), and both bonded just fine. I don't think the age you get them at is what matters, but rather their past experiences with humans. I think the reason people say babies bond better is because when you get a baby it's more of a blank slate and more impressionable, and you are raising it in a way, versus getting an adult that has already been accustomed to a certain way of interacting with humans and might need to be retrained if those interactions were bad.