My impression from mates who work as PT staff at ATR's is that recruit entry level fitness standards are p1ss p00r and continually declining as the general population becomes more sedentary.
That said, the better you are at the start, the less you'll get fragged to acheive the minimum standards so don't use that as an excuse not to work on your phys.
Sounds like you're fairly active so give yourself a good head start by getting yourself down to sub 10 mins on a mile and a half, learn how to do 60 PROPER press ups and 120 good sit ups and keep yourself there until you start. The PTI's will take you from there. There's no use fragging yourself before you get there.
edited to add: unless you have aspirations to the infantry, in which case you will want to reduce that mile and a half time by a little more. and a lot more if you think you want a piece of that PARA/Cdo action.