Board Thread:New on Ben 10 Wiki/@comment-24579099-20140701182447/@comment-34326521-20141013101531

Ultimatewrath wrote: if he was 23 he probably would be taller and more musclar then 16 year old ben but he is not so that makes him 13 Or... you know... literally any other age between 10 and 16.

Seriously, there's no proof that he's 13, nor is there any evidence for it, unless you include a bizarrely misinterpreted comment by Ben 23.