A Diamond Jubilee [ or anniversary for a marriage] .
Centinial
A period of 75 years is called a "septuagenary."
After years of hard work and dedication, she finally achieved the completion of her PhD thesis.
A Century, is the completion of 100 years.
it's called "old age" middle age is 40-60 years .
75 years old
They have by being called mixed
75 years is equivalent to 3/4 of a century
4.9 years
75 percent
There is no star that fits that criteria. Are you maybe thinking of Hally's comet which is seen once every 75 -> 76 years? See related questions.
For the passer, it's called a completion. For the receiver, it's called a reception.