Convert both dates to seconds since epoch (%Es), find the difference, then convert back to years. If you don't need to take leap years into account, the easiest is to divide by 31556952 (the number of seconds in a non-leap year).

Or to be completely accurate (using leap years and all), first convert the dates to FME timestamps then use the DateTimeCalculator:

I'd probably use the Date/Time Functions, so parse the attribute named birthdate into date format, calculate the difference in years from today's date and round down

@floor(@DateTimeDiff(@DateTimeNow(),@DateTimeParse(@Value(birthdate),%Y-%m-%d),Years))

Nice I didn't know we could do that :D

I need to put an AttributeRounder after to take out de decimals though.

Thanks!!