Not all cats will be lapcats, but give it time and gain it's trust and it might come and lay beside you and eventually lay ontop of you. If it feels stressed it might feel it's not rewarding to lay on your lap, so don't force the cat, but once it comes near you make it feel it's comfy and nice in your lap and soon you'll be complaining it's not laying beside you instead.
Pick him up, but not every time you see him, or when he comes up to you. Sometimes talk to him, stroke him, or pay no attention at all. If he comes to you just give him a smooth, dont pick him up and put him on you.
He's still pretty young, too, so he may get more settled and lappish with age. IMO, there are a lot of cats that very much prefer to approach people on their terms, and if you approach them and pick them up, it can offend their personal kittycat space.
Make sure that you're making "good laps" (without slippery or strange fabrics...Assumpta is partial to flannel), and that when the cat DOES get on your lap, that it's a stable and unthreatening one. Resist the urge to pat immediately, or wait until the cat asks for it...let the cat explore and find a good place to sit, and then STAY there (if at all possible) until the cat decides it's done (this may entail missing a couple of phone calls). If you're a fidgety person who is up and down a lot, it tends to deter a cat from wanting to lie there. After dinner is usually a good time to attempt this (Assumpta always wants a "digestion lap").
I've found that there are certain situations where my kitten will come and lay in my lap. One is when i am in the office and she lays on my lap as I am typing on the computer and the other is at bed time.
Other than that, she spends ALL of her time running up and down the couch chasing our 4 year old cat around the apartment and playing with everything in sight. I think it does have to do with the age. She comes over and lays down on me for a minute or two but is too easily distracted and runs off. So, I don't think it's because of trust or being scared or uncomfortable. I really think it's just because at that age they are like 5 year olds and everything is just so much fun!
Don't be offended, I think your kitty will come around.