The Perfect Tenses" (Brian Rhodes)

Remember, in grammatical terms, perfect means completed or finished.
Usually, the present perfect tense uses since or for to help in telling us when it occurred:
a) I have lived here since 1990.
b) I have lived here for 12 years.
Use "since" when you are telling us the date; use for when telling us how long.
A lot of English speakers use the simple past instead of the past perfect. Compare:
a) Before I came here, I never studied grammar.
b) Before I came here, I had never studied grammar.
Usually the future perfect and past perfect are in need of being set up in the time line with adverbials such as: by the time... before... etc.
Notice the verb tenses:
By the time I turn sixty, I will have had many years of enjoyment.