Is 3 years old too young to go snow sledding?

My son just went sledding down hill with friends. He was the youngest kid sledding, but he was a natural. He is 3 1/2 years old but looks like he's 4 1/2 cuz he's big for his age. I told a friend of mine that my son went sledding and she said "gurl you gotta watch all that sledding". Don't you think it's fine for a 3 1/2 year old to sled down a really small hill with his neighborhood friends?