Having said you want to be Navy specific DEU, only my belief here; You may want to look at something other than Steward as that one tends to fill quick. I don't know what your back ground or current 'hobbies' are but trades like Stoker, ET, NE and NW Techs are always short. I have seen several people in your age group join and they tend to bring something unique to the group. Last year following the Consecration of the Queen's Colour, out of all those people involved, when the group was asked to nominate one individual who contributed the most to the group, it was a 'mature' sailor(Ordinary Seaman).
You will find somewhere on here the pre-reqs for fitness, but if that is all that is holding you up, do not be overly concerned-There are programs within the CF. One of the Mods may have the overwhelming desire to butt stroke me after having answered you after a recommendation to search through the other threads but I am in your age group and am tired of trying to keep up with the 20 year olds in foreign ports-I need some company man!!!!