There's two questions here, Ripley's objective age (e.g. the difference between her birth-date and the date of the film) and her subjective age (e.g. how old she is taking into account time dilation and hypersleep). I'll address them both.
This is the easy one. Her DOB is given in a Special Edition DVD feature as January 7th, 2092. We know from the novelisation that Fiorina is only a few days travel from Gateway, which strongly implies that she was only in hypersleep for a few weeks between the ending of Aliens and the start of Alien³. Since we know that Aliens takes place in 2179 (July, 2179 to be precise), that makes Ripley 87 years of age at the ending of Alien³
This one is a toughie because there's a few unknowns. In theory, she's subjectively 32 years of age throughout the events of Alien, Aliens and Alien³ (born 2092, shipped out 2124) but we don't really get much backstory to explain how much time she's spent in hypersleep since birth, nor do we know how much one ages during hypersleep. Certainly she appears to have aged, but that could just be down to stress.