Often, to determine which tense is used in a given question, we simply need to remember which question words are used with which tenses.
Compare when….?( + past simple) and how long….?(+ present perfect):
For example:
A: When did it start raining?
B: It started raining an hour ago/ at 1 o'clock
A: How long has it been raining?
B: It's been raining for an hour/ since 1 o'clock
For example:
A: When did Joe and Carol first meet?
B: They first met a long time ago/ when they were at school
A: How long have they known each other?
B: They've known each other for a long time/ since they were at school.
We say 'It's ( a long time/ two years) since something happened':
For example:
It's two years since I last saw Joe ( = I haven't seen Joe for two years)
It's ages since we went to the cinema. ( = We haven't been to the cinema for ages)
You can ask 'How long is it since…?':
For example:
How long is it since you last saw Joe? (= When did you last see Joe?)
How long is it since Mrs Hill died? (= When did Mrs Hill die?)
You can also say 'It's been (= It has been)………since………….':
For example:
It's been two years since I last saw Joe.