FOR AND SINCE

We use Present Perfect tense to talk about action which started in the past and continues up to the present.


Examples
   I have had this computer for about a year.
   How long have you been at this school?
   I haven't seen Julia since September.


Tip! For other uses of the Present Perfect tense, see the Present Perfect Tense - When To Use.


We use for with a period of time, for example: a few days, half an hour, two years. We use since with the time when the action started, for example: last year, June 8, I met you.

http://www.eclecticenglish.com/grammar/PresentPerfect1D.html

http://www.ejerciciodeingles.com/ejercicios-present-perfect-for-since-ago-rellenar-huecos/