Present perfect continuous with FOR and SINCE

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

I've been waiting for you for ages.
He has been living here since last week.
"How long have you been learning Spanish?" "For two months."
"Since when have they been dating?" "Since October."

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

He has been living here since he started school.
They have been dating since they first met last May.