It could depend on whether you are on a Hollywood or Hell platoon. You won't know what you are on until a few weeks in, and staff won't call it one or the other.
A hell platoon is hell. It feels like punishment PT for breathing out of sync, etc.
A Hollywood platoon is the kind that seems to not do PT except for the fitness testing.
Many platoons are somewhere in between. It depends on how your platoons comes together. If you meet your timings, straighten out the shit pumps without involving the staff, etc, you should have a good time.
You could have instructors that just like to run however. Staff that are Vandoos love their morning runs. And afternoon runs. And weekend runs. Just don't stop running because you feel a twinge in your knee. You will be spending the rest of the morning/day at the MIR and if you get a chit which excuses you from running, you may end up bearing a lot of instructors' frustrations. If you have real pain, then go. But make sure it is REAL pain, not just age.