My DS3 was not really crawling at 8 months old, and making no attempt to stand but he was vocal and developing in all other areas. At his 8 month check he was refered to physio and diagnosed with benign congenital hypertonia (his muscles were too elastic, he had trouble controlling them, common condition among contortionists) and with physio he was actually walking at 16 months.
A friend of mine's DS (1st and only) turned 1yo last week. He doesn't really make any sounds, grab things that are slightly out of reach, crawl, roll over or attempt to move in any way. He doesn't look like anything is wrong iykwim, and I don't really know if she took him for his health checks, she said she has. I know she has very limited baby experience (she is an only child and so is DH, her cousins are all older than her or around the same age). She is the first parent among them too. It's just that I know I was concerned about DS3 at 8 months. She just says that her DS is lazy.