Present perfect with FOR and SINCE

The question words how long? and since when?, and the prepositions for and since are used with the present perfect tense to express that something started in the past and is still true. How long? and for refer to an incomplete period of time, while since when? and since refer to a point in time:

I have lived here for two months.
I have lived here since January.
"How long have you known José?" "For ten years."
"Since when have you known José?" "Since the early 1990s."

The point in time after since can also be expressed with a clause containing a verb in the past simple:

I have lived here since I was born.
I've known José since we were young.