Based on going through a bunch of "Word of Jim" posts (someone on the spoiler board has collected practically every post that Jim has made on the Dresden file - and has sorted them by topic) I think I know the answer to this one.
A were's lifespan is whatever it has to be for Jim to write a kick ass story. And since all it takes is for Harry (or Bob) to say "these were spirit animals awaken, those were hit by a spell, that kind were played with by fairies, etc" Jim can make as many different types of weres as he needs to. If he thinks it would be cool to have a wolfwere with a human lifespan fall in love with one that has a wolf lifespan, then that's what is going to happen (a tragic, doomed loved in the Dresden Files? It fits).
Personally, I think Terra's son (who becomes a monster on the night of the full moon) will be in a later book - maybe even the BAT. No, there is no proof that she was pregnant at the end of Fool Moon, but I think she was because the curse has to continue until the Judgment Day. Will he be a grown man in the next book (i.e. aging by wolf years)? That could happen, but I doubt it because of the subject matter of the next book. But maybe the book after that. Or maybe he'll be in the BAT - which implies aging by human years.
Until we see him again, it's whatever the group decides. Personally, I'd go with "wolf years until they start to change, human ones after that, and in special cases - unaging".
Richard