In addition, G tolerance is governed by the distance the brain is away from the larger of the major blood pumping organs of the body! With most people of your age this distance is quite large (and unless corrected can lead to blindness and hairy palms!). In taller people, the heart has to work far harder, under G forces, to get the blood to the brain.
I was a nav on GR1's and, at 6'4''/193cms, was taller than average.
My personal grey/black out limit seemed to be about 4-4.5, dependant on the pilot telling me when he was going to pull some G's, so that I was prepared and could strain against it. I remember one trip at Chivenor, during my Hawk training course, flying with Tom Leckey-Thompson as baggage in his boot during a staff 4v1, when I spent the entire 45 mins unconcious! He took off, loaded up the G's and that was it, 3P asleep in the boot.
I concur with the coments about fitness, I wasn't, I smoked like a bonfire and drank far too much to be as fit as I should have been at that period of my life (it got worse later in Germany).
You will be fine, trust me.
3P