First of all, thank you for rescuing this kitty! It's tough to remember, but unlike dogs, cats are just not programmed to like or want to be liked by humans. Like Hissy said, it's an issue of building trust, which simply takes time, especially with feral (formerly wild) cats.
It could also be that he's teething. Cats get their adult teeth in somewhere between 4 months and 6 months. Get regular-sized bendy straws, and scatter them about your house, especially where he hangs out and you play with him. He can chew these (and will), but he can't chew through them like with hard plastic, so he won't end up swallowing little bits (before you see the straw has many holes in it and needs to be replaced).
Also, I don't know if you're playing with him with your hands (or feet), but that is simply a no-no. Don't. It's cute and fun when they're small - until they begin to bite. And then they get big. And for now - stop trying to pet him. At this point, if you're not playing with him (with a wand toy), basically ignore him.
The fastest way to change his behavior is to let him have his space. In essense, start over with this little guy, and treat him like a feral that needs to be socialized. Encourage play with wand toys, but any other interaction - other than a "head-bump" from him
wanting pets, should result in you blowing a short sharp puff of air in his face, followed with a stern "no" (not in a raised voice). If he's playing, and nipping at your ankles or fingers/hands, lean down, give the puff, say no, and grab a straw to play with him. Same thing if you're walking past him and he tries to nip at your ankels or feet. But DO NOT do this if he bites you when you reach out to pet him. His biting is the only way he can communicate with you that he doesn't want to be petted.
The problem isn't that he's biting you when you try to pet him, the problem is that you're trying to pet him when he doesn't want to be petted.
But in the meantime, he'll quickly learn that biting is not acceptable.
Take a quick read of some of the other threads in this forum about socializing kittens. The basic requirement of you is patience, and his basic need is space. And, quite frankly, the more you ignore him when you're not playing with a wand toy, the more comfortable he'll get more quickly. Especially if you have other cats, and he sees your interaction with them. At some point, his curiousity will get the best of him.
In the meantime, you can also take a sweatshirt or t-shirt and do something while wearing it to get it good and sweaty. Place this under his food dish. This will help him come to associate good things with your scent. You can do the same thing, but place treats on it for him. And just leave it - walk away.
I have no doubt that he'll wind up as a wonderful pet. All of our six cats are feral rescues. But they take time - you have to earn their trust. And even though he wanted love and cuddles as a baby, now that he's a teen, he apparently doesn't want those same hands reaching out at him.
There are many things you can do to work on his socialization. But the bulk of them involve basically ignoring him until he comes to you again - but being around him NOT looking at him, NOT trying to pet him, NOT searching him out to see where he is - just being around him, ignoring him, until he learns you don't want anything from him but to take care of his needs - which will then, eventually, include his wanting to be loved by you.