Gliders are very scent oriented animals and it is not a good idea to just bring home a new glider and immediately put it with the gliders already in your home.
A 30 day quarantine - housing them separately and in separate rooms - with no contact between the gliders is recommended with the new glider having a well check up and fecal testing done soon after coming to you and a repeat fecal testing 30 days later to make sure the new glider is not bringing any parasite issues to share with your first glider.
If your first glider has not had a well check up and fecal testing - that should also be done before introductions.
After the quarantine period then you begin swapping pouches and toys between the two cages to gradually get both gliders familiar with the scent of the other glider before you do a face to face introduction of the two gliders.
If both gliders are young introductions are fairly easy but since your current male joey is now about 4 months OOP - if he has not been neutered he is beginning to mature and may begin to be territorial.
If the second glider is female - he should be neutered BEFORE you introduce them to prevent breeding. If you are planning on breeding the two gliders should not be introduced until the female is at least 10 or 11 months OOP to prevent them from breeding before she is a year old and mature enough to raise healthy joeys.
If the second glider is male - I would have both gliders neutered before doing introductions to reduce the chance that they will fight as both mature. It will also reduce the pungent odor that intact male gliders have especially when trying to out mark each other in a shared cage. Your house can get very smelly quickly.