How old are Jessie and James in Pokemon?

I agree, I've heard that they're both 17. Which could be more right as Jessie says so in the anime.

It's most likely that they're around 17 or 18. Seeing as, in the beginning, Ash was 11, Misty probably around 12 or 13 and Brock was 15, I can't see Jessie and James being that much older..