For or Since?

For/since

FOR    and   SINCE    are   used   to express   time FOR  denotes the whole period of time ( duration) : for one year -    for two weeks - for a long time -                  for  three months  SINCE  only shows the moment when the action started (a specific time) :   since last Monday                        since I was born  -

For is used to refer to the whole period of time:

• I've had this watch for more than 40 years.
• I've only known her for a few weeks.
• He's been here for 6 months and still can't speak a word of German.
• She's been smoking for a long time. No wonder she coughs so much!

Since is used when specifying the starting point:

• I've had this watch since 1965.
• I've only known her since the beginning of last week.
• He's been here since April and he still can't speak a word of German.
• She's been smoking since she started grade 5. No wonder she coughs so much!

http://www.englishexercises.org/makeagame/viewgame.asp?id=5876

http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/upperf1.htm

http://www.ego4u.com/en/cram-up/vocabulary/since-for

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