Hi LynnMarie, welcome to the forum.
GOOD FOR YOU saving that little bird.So many would have just driven right by. Poor thing.
There is a way to sort of determine age by the irises.
Here is a link to a site with pretty good explanation and photos that might help you out.http://www.budgieplace.com/age.html
I wish the boys at the pet store you went to didn't clip his wings, but what's done is done. They will grow back with his next molt but until then, like illusive said..be very careful holding him at too great a height and if you let him come out of his cage be sure there is a way for him to get back in. The cage itself should not be set too high if he is allowed out by himself just in case he tries to fly and can't.
In fact you shouldn't even let him out until he is used to you and hand/finger tame.Give it time
Hopefully they didn't trim his wings in such a way that he's not even able to glide to land if he needs to.
Get as big of a cage as you can afford. At least 30x18x18high...better yet 30x18x36high. Bar spacing needs to be 3/8-1/2"
It might sound big to you, but really by the time you get a variety of perches, different diameters..which they need to keep their feet healthy. For instance comfy rope perch, natural branch perches are awesome(you can make your own from bird safe/NON TOXIC branches- http://www.parrot-and-conure-world.com/non-toxic-for-birds.html
and conditioning perches for nails n beaks are a must-like the cement/shell perches here- http://www.birdguys.com/bird-conditioning-perch.html.
The ones that go all the way across the cage.
*the ones that only stick out part way can be dangerous if bird should happen to have a night fright or freak out and fly around in cage they can easily bump in to it and injure themselves.
Toys, swing, food and water cups....it doesn't leave much room for your bird to fly, play, and stretch his wings.
So if possible, don't make the same mistake I did and get a smaller cage only to realize you need a bigger one. My bird's first cage was something like 18x20x24H. Looked plenty big enough until I started adding things to it. They need toys to play with, things to stimulate their minds and keep them from being bored.
No need to get him a buddy. He'll be perfectly happy with you and your family as his flock. In fact if you get another it will be sooo much harder to bond with and train this one. Not to mention you can never be sure of the gender of the new one and can end up with breeding issues.
It's perfectly normal for him to be quiet at first. It's all new to him, he's scared. Even those coming from the pet store or even a breeder are quiet for a few days...and this little one has been thru sooo much more. Poor kid
Even tho he might be perching on your finger now, it doesn't mean he's used to you or trusts you yet. He is probably just too scared to put up a fuss about it. So don't be surprised if that changes and he shies away, that's okay.
Let him get used to his new home and family before you even attempt to get him to step up.
Congrats on your new found friend. If you take the time, take things very very slowly, never force him to do things, earn his trust...I think you will find these little ones to be sooo much smarter and more fun than you ever realized.
We'd love to see pics
Oh and one more thing? Leave a night light on for him