I am trying to calculate the investment total at given ages and APRs. I know I am using a FV formula but I am having difficulties with the NPER portion. I am given the ages workers plan to start investing, but I am given a retirement date. Is there anyway in excel I can subtract the date from age so I can get the actual term(or period) length.

(EX. Start age= 23, Retire Date= 4/11/2047, Initial Investment = $5000, Monthly Investment =$75)

I AM STUCK, PLEASE HELP

THANKS!