Good morning, Catherine-
Will a slightly more simplistic view work? I mocked up a formula with
three columns: a header in A2 that says "Start date"; a header in B2
that says "Employed Years", and a header in C2 that says "Vacation
days". In A3 I used your sample date, March 15 2000. I used this
formula in B3:
=(TODAY()-A3)/365
.... which generates a fractional number of years the employee has
worked. This is the oversimplification: it assumes 365 days in every
years, which is not always the case but arguably has little impact on
the intent of the calculation.

The formula in C3 is
=IF(B3<2,20,IF(AND(B3=2,B3<=5),22,IF(B35,25,"")) )
.... which tells the allowed number of vacation days.

Does that do it for you?