Being only a little scamp myself I'm in no position to talk through experience but I seem to recall being told that airlines look to get at least 12 years out of you which would be enough to make it worth their while so you're perfectly ok with mid-thirties. Also some airlines actually prefer the older guys and wont take people under 28 (although thats not a legal policy of course so its not official and they wont tell you that, they just 'prefer' the older guys) all to do with life experience or something rediculous like that
Why shouldn't they like young guys?! I'm indestructable and I do actually know everything there is to know!! ahem.
Good luck