It depends on his foot size, some feet grow fast and some don't. My grandson wears a size 8 and 8.5 and he is 2 years old. He was 17 months when he wore the 7.
As far as sizing, my grandson is just now going into a 7. He turned 2 on Feb. 13th. (He can still wear some of his size 6.5 ones. It all depends on the brand.) Great auction. Plain white would definitely come in handy.