On a small scale, you do not need a license.
No set age limit, but IMO you should not attempt it any time soon. I know about your situation, and it would be much too hard to start taking in rescues right away, after only have gliders for a very short time.
Well, you need the cost of cages (but you still need to buy a bigger one for your pair now),
toys,
vet checks, any other
vet bills (they can and will pile up quickly if you jump into rescuing), food, neutering, etc. Rescuing is VERY expensinve, and it really shouldn't be done until you have a lot more experience with gliders and are in a more stable situation.
You're not even a month into glider ownership, correct? I really think that you need to step back and not look for any other gliders right now, especially not rescues. Just spend this time getting to know your gliders, how to handle them, get into a rhythm with them. In your place right now, you probably would get in way over your head. You don't have your own place, so eventually you will run out of room and will have to turn gliders away. Do you have just one room to keep the gliders in? You will need at LEAST 2, for quarantines. You would be the only rescuer in western NY, so guess who all the gliders would be going to! You don't have a job, and rescues can be a lot more expensive than a joey (not always, but they can be). Last I knew, you still hadn't found a
vet. When you get a rescue, the first thing that needs to happen is a wellness check. You also need to have a
vet on hand 24 hours, because a rescue might come to you with serious health problems. I know that you are looking for a bigger cage for your pair right now, will you be able to afford getting a new cage each time you get a rescue in? While some might come with cages, there's the chance that they are no good for gliders anyway.
Those are just the physical things that might hold you back. How about emotional? Can you handle trying to save a sick glider, rushing it to the
vet, but having it die after you spend $1000, withing the first week of having it? Will you be able to deal with a glider who attacks anything that comes near his cage, because the poor little guy has never had any interaction other than being poked and squeezed?
Not all rescues are like that, but those are things that DO happen. Are you absolutely sure you can/want to handle all that on a regular basis?
I really think you need to slow down, and work out all the little bugs you are having with your own gliders right now. You're doing good, but there's room for improvement, and you know that. Just take the time to
bond with your gliders and spoil them silly. I'm not trying to discourage you from rescuing, but you need to know what you are getting into. It can be very rewarding at times, but it can also be stressful and heartwrenching and expensive. I think it would be best if you waited for awhile. I mean a few years, you are young, you've got plenty of time.