Both sentences convey a different meaning. Why?

I have a friend who is only 15 years old. Since he started working hard.

  Why do the words "time frame" say nothing about an event?  

Still (adverb):

  up to and including the present or the time mentioned; even now, as formerly. "He still lives with his mother" synonyms: up to this time, up to the present time, until now, even now, yet I understand he's still married to her antonyms: no longer referring to something that will or may happen in the future. "We could still win"  

Despite being old, he still works hard to improve his quality of life.

  In this sentence you would say that up to the present time the man is working and that the one likes getting out of the work.  

How do you describe yourself to an individual?