Something to also consider for a weakness would be magic, since he can't use it, it's often hard for sword wielders to counter magic attacks. Not only that about magical attacks on the mind can be done as well. And what about strength? Is it a weakness? Not very strong but fast? A 17-year-old boy's muscles are not very developed yet, so he would have the disadvantage against a strong adult. Develop more on my suggestions

And the last thing ... please don't do the "revenge for my dead parent/mentor" bit. Try to think of a more original past.

__________________
Pagan Club!
[The Figments of My Imagination]
"We fear that which we cannot see." ~ Bleach
[Between the Worlds | Empire of Darkness | A Light in the Dark | In His Shadow]