Когда говорим о том, что произошло в течении какого-то времени, используем for:
two years
an hour
a month
a long time
days
Когда указываем с какого времени что-то произошло используем
since:
Cristmas
1999
Saturday
I was 11
last weekend
Ex. e
I have studied English since I was 11 years old.
They have been married for 20 years.
Ivan has had his bycicl since 2001.
I haven't seen Mark for ages.
Maria hasn't spoken to John since yesterday