I just want him to be as he was once he was young.
That's your issue right there, he's not a puppy, with puppy licence, he's not an adolescent who will be taught boundaries by other dogs he meets (the stage where he should
have been on a long line, the most dangerous time to be attacked and scarred for life, moulding the dogs perception of other dogs, also the time he could hurt smaller dogs.)
He's an adult now, his alliance is now to his owner, he won't be interested in playing with other dogs (much) so don't worry about that, that time may well and truly be over, don't think of it.
He may wish to meet and greet if he has had no bad experiences, but unfortunately you allowed him to get into altercations (you may have judged them not serious, but they define his character)
He's no longer sure if a dog he meets is going to growl at him or play with him, so he may well become defensive, he's too big to take the chance, so please use that long line until he settles 6-12 months.... GSD's go through stages as all dogs, they play, become unsure, worried, think they're the big man, then fine, then, don't give a toss about other dogs......
Concentrate on playing with him and keeping his focus on you, have fun yourselves on walks.... The KC bronze, silver and gold are fun to do along with activity groups great bonding for you and your dog if your interested.
If you allow no confrontations, he'll settle and be a lovely boy again, and get to the 'I don't give a toss stage' then you'll think he's got boring.