Hi J.!
Your son sounds just like mine did! My son was so advanced in his gross motor skills, that I think he didn't have 'time' or take the time to learn all of those things. He had a small vocabulary at that age, where my daughter was speaking in full five words sentences at that age. My children are 19 months apart and they are now learning shapes, colors, numbers at the same time. My son is almost four. He just never seems interested. I do try and he hears all of these things on a daily basis,as I have an in-home daycare where we have daily activites involving letters, numbers, etc. I just think it depends on the child. It is hard not to compare children, especially family members and friends, but please know that children all learn at their own pace. I have a 22 month old in my care that came to me with about 10 words in his vocablulary, most of those pertaining to names of different sports. He now says so many words and learns about five or six new words everyday while in my care.
I don't think that you have to sit down and do flashcards with your son, but implement some daily activities involving learning. Count peas on his plate, talk about what color they are, cut out different shapes and colors out of paper and let him glue them onto paper. He will get it eventually. Children have the rest of their lives to learn and yes, it is important in their early years, but I don't feel that we as parents should stress about what they know or don't know. Make learning fun and the rest will follow. He is probably more advanced in other areas than your friends child anyway. I have a friend whose son can not take direction of any sort, but can talk up a storm. My son, on the other hand, could crawl to his room, get his diaper out of the cupboard and bring it to me at ten months old. Please let me know if you have any other questions, I am more than happy to help:)
-Janelle