I adopted a young adult female cat (estimated to be 2 years old at the time) from the street, probably a dumped pet (not feral). She was very skittish at first and never did sit in my lap in the following 14 years, but gradually over time she got comfortable sitting next to me. I've adopted other adult cats who were sitting in my lap within weeks (or days), so it's not a kitten-versus-adult thing. Every cat is an individual with its own background, and when we adopt we usually don't have any clues about that background.
With my reluctant cat I found that the worst thing to do was to pick her up and put her in my lap (or even just hold her). Picking her up triggered an "aiiieee! I'm not in control! Run away!" reaction. I sometimes sat down next to her (if she was, say, lounging on the couch); I moved slowly and avoided any sudden movement or noise, and that allowed me to sit next to her and pet her. Eventually she started coming to sit next to me, which I rewarded if I could (I kept a bag of treats near my favorite chair for a while). I also pet her gently when she did this, just as I did if I sat next to her.
This is a long, slow process that is based on building trust. Anything you do to alarm your cat will set you back. Some cats may never sit in your lap, but others will eventually. Take it on your cat's terms.