My guess was going to be around his early thirties and that does tie in reasonably well with my supposition that Rimmer went more or less straight into the JMC from finishing his education (I'd presume that he didn't pass or got booted off whatever further education courses he took otherwise I'd assume he'd have those certificates on display alongside his swimming certificates), although I think the only time a character's age is actually mentioned in the show is in Lister's preamble to Tikka to Ride.* I wouldn't take an actor's age as anything other than a ball-park indication of roughly what sort of age the character is supposed to be. Personally I took Chris Barrie to be somewhere between a mature looking mid-20s and a youthful looking mid-30s in The End, a pretty wide ball-park I admit, but I think that's about as much of a guess as you can reasonably make. As an aside, I'm sure I can recall someone doing the maths on Kochanski based on Lister's comments in Entangled and working out that she should be about 11 in The End! So either the JMC does employ children (as officers no less) and Grogan-Kochanski was incredibly physically mature for her age, or yeah, Maths really isn't Doug's strong suit. (Or C: It's a sitcom and they really didn't think it was that important) * Edit: And Kochanski, possibly erroneously, in Entangled.