I'm also learning Korean, but here's what I think. :) This is a bit formal, though, I think!
저는 스물세 살입니다.
jeo-neun seu-mul-se sal-im-ni-da.
I am 23 years old.
Roughly:
저는 (jeo-neun) = I
스물세 (seu-mul-se) = 23
살 (sal) = age marker
입니다 (im-ni-da) = to be [am]
EDIT: Sarah's comment adds more. :)