I have only ever played CQB. First time I went, in the very first round I took a BB directly to the second joint on my index finger (I suspect this gun was also hot FPS wise) and it instantly ballooned to nearly double (no joking here) the size. As it was my first time I'd neglected to wear gloves seen as I thought it was probably unlikely I'd take a hit there. But alas I did and I donned my extremely non dextrous motorcycle gloves and limped through the rest of the day. I loved it though, but first on the list of things to do when I got home was decent gloves, eye pro/face mask and an armoured baseball cap, because I can also tell you getting shot in the forehead from 5 feet away with a 350fps gun does smart like holy hell.
Whether it hurts or not is subjective, I've taken many a shot that I genuinley didn't feel, and others that have stung like hell. I nearly lost the bottom of an earlobe to a shot recently. Looked like I'd had an amateur self piercing incident.
I'd say 8 is too young for a full bore game, 11 is debatable but if mature enough to wear a bit of sting without flouncing then I say go for it. Outdoors fields with minimum engagement distances are also fairly friendly toward younger players.
I would not go near a CQB though. Haha.