It may be a little too early yet. My son didn't start sitting unassisted until almost 7 months old then he was crawling the next day. The biggest thing that helped him to sit up was I got him an activity cube for Christmas and he would play with it sitting up holding on to it with one hand. Then he eventually let go.

Physical therapists will tell you to avoid the chair. The baby has to develop their abdomen muscles on their own by crawling, rolling, practicing. My daughter will be 7 months next week and is just now starting to balance when I place her into sitting position.

What kind of chair do you have for him?

He will sit when he has enough muscle strength. Let him practice crawling and he will get to siting - those come hand in hand. @babyshreiner16

Mine wants to stand too. His sister never really crawled either. He is trying to sit as well. Flips from belly to back, but not the other way. I think that's because he hates being on his stomach. Lol @raisinghazel

All babies are diff he'll learn eventually. My daughter has no interest in crawling only standing and walking. She still can't roll from being on her back.