[Lucid:]

I...have the same issues with drawing ages as well, so there's not much advice I can give you on that aside from look at cartoons to see what features other artists emphasize to express age. I think the Avatar/Legend of Korra series is really good at drawing different ages.

As for your characters' ages....
I think Storm looks 26.
I think sin archer looks 23.
I think sin merc looks in his early 40's.
I think guard looks 19.
I think Kienra looks 30-ish.
I think Lunis looks 15.