Or to give equal time, people can ignore the line about being just 17 in ST09.
No, they can't. Walter Koenig was 30 when he did "Who Mourns for Adonais," so it's just as easy -- maybe even easier -- to accept him as 26 in that episode as the stated 22. But there's no possible way to accept Yelchin's Chekov as only 13. It's hardly a symmetrical situation.