#10 - Oh Dear! - this just shows the problems that could arise between buyers from different countries, doesn't it?
'Junior small' would indicate absolutely NOTHING to a UK buyer - mind you, the 'ages' thing is just as vague.
Length and chest measurement (In inches/cm) is, I feel, more reliable, and could be standard across all the various eBid sites.

It would need a fair bit of category expansion though!