When Does A Baby Start To Crawl?

Question : Hello Doctor, I am mother of 4 months and 10 days old baby boy. 1. My son is rolling over the tummy from both right and left side. 2. He can lift his head for few minutes with balance on his elbows. 3. He can distinguish familiar and non-familiar faces 4. He loves to go around for evening walks 5. He is with lot of sweets coos and his talks. 6. He is trying to life both his legs using his hands 7. He can hold object using both the hands. In general he is a healthy boy. But many people tell me that by this time he should have been crawling. I am observing one thing after rolling over he tries to crawl. But then he starts biting/sucking his fingers and end up in crying. Many times as results of putting fingers in mouth he vomits also. I tried encouraging him showing some toys, he likes to catch them but does not put any effort. Do you feel I need to give any special attention or all these things normal? Regards XXXXXXX

Hello doctor, Thanks for the reply. My kid usually indicate hunger by putting only one finger in mouth. But while he is on his tummy and trying to crawl, he stars biting his fingers and tries to push fingers into mouth and then vomits some times (I think that is expected as he pushes too much inside). This made me think if I need to worry about building up strength in the arms. Regards XXXXXXX