Just to be clear, it's not so much a question of age so much as a question of easy integration into the ongoing story. A roleplaying game is like a story we tell each other, and nothing ruins a story or a movie faster (for me at least) than things that don't make In Character sense (i.e. characters acting out of character for no visible reasons).
Sadly, the worst offender in roleplaying games is usually integration of new PCs: the 'you're a PC too? Join our group then' syndrome, or the much dreaded 'why do we adventure with this jerk exactly?' with no other possible answer than 'because he's a PC'. (I've had at least one game nearly go down in flames because of this, so I might be more sensitive to it than others, but there you have it.) So play a full grown adult or an octogenarian or a three ton goblin giant, Alkaline, doesn't really matter so long as he or she has a good reason(s) for wanting to adventure/associate with the other PCs, and they have good reasons to associate with him or her. You'll be much happier with clearly defined place in the scheme of things, trust me
.
So my question, I guess, then becomes: why would a fully grown professional criminal associate with idealistic teenagers (well, at least two of them are idealistic -- three if you count Mysthyr, in his own way
) who are likely not going to specifically hire him for his services -- especially if they ever find out about the 'criminal' part?
[sblock=My take (entirely optional)]If we say that our goal is to design a character that's likely to be joining the main party (and be happy there), I would personnaly suggest turning back the clock on your PC a bit: don't just make him 18, turn him back to how he was when he was 18: thrill seeker, tried a few stunts/stealing, but not yet chosen a criminal carreer. Trying to join an adventuring company that's just made a splash/he's just heard about could make a lot of sense then, especially if he knows (however vaguely) one of the existing members (dealer's choice which one
).
I'd also suggest giving him a reason to be in Askadar, specifically. This could go by way of tweaking his background to make his hometown Askadar (there's bound to be lakes and rivers nearby, right? (big ones? would have to ask Gambler), so he can still come from a fisherman background, with maybe even his pa/grandpa/'uncle'/actual aunt having actually sailed on the brimy seas and regaling him with incredible stories if you still want to have those in place?), or his parents can have (a few years ago/relatively recently?) moved from Osvale to Askadar, for whatever reason, taking Wilben with them? Seeking something specific here is also a possibility (say a relative that, it turns out, has been disappeared by the White Things? That could give you a very good reason indeed to get deeply interrested in what the party is doing.). Mix and match as needed.
That way he has both motivation to join and a reason to be there to have the opportunity
to join.
(And I
still think two thieves would make for some very interresting stories! But that's entirely up to you, Gambler and Whizbang, of course
)[/sblock]
