How many years from start date formula

The DATEDIF formula is a bit of a special story.. it is officially not supported in excel and therefor not in the list of formula's (I believe there were lawsuits against MS for copyright infringements)
it is however available in the background but you will have to know (or find on internet) how to use it as the normal help to setup the formula is not available

It is the right formula to use however..
I also put a small lookup table for the year ranges that is easier then nested if formula's

Edit: I see humdingaling in post #2 also posted a link, that link has a clear list of available options, make sure to check that is you also want months or days sincs start