Half a century or five decades
That's called a millenium.
The simple interest over a period of five years is $463.70
It COULD be called a Gigayear, but in practice it is simply called "a billion years".
tu hola
a five-year period is a quinquennium
What funds are available for new obligations for a period of five years
The Gram Panchayat functions for a period five years.
A period of seven years is called a septennium.
There is no widely used term for such a period.
generation
sevennenium
100 years is a "century."
It's just five years, but you could say "Half a decade" if you want to be fancy.
a silver jubilee
A golden jubilee
term millennium