Are they growing too fast?

This is not quick I'm afraid my friend I have plants that are the same age and they are huge compared to this lady though that's nothing really to brag about it just proves that you are using the nutes correctly and also have all your balances dialed in. As the other grower has stated you should take a look around grow diaries there are people out there with very short diary times im talking like 9 weeks from start to finish now thats quick though these grows I fear do lack the yield most are after. best thing about photo period phenotypes are that you are in complete control as to how high she gets how many tops she has and how much space she takes up. 3 more weeks veg I would say would be about right for a full blown plant that is going to produce a some what respectable yield I can only go from my own experience and none of what I am saying is law it is just advice and should be treated as such :) though she is looking really healthy I would advise only using the netting after you flip them with them already having the soil as a medium they dont need the extra support at the moment I would revert to tieing her down instead then add the net in the first or 2nd week of flower after the stretch then you can really space the tops out and get that even flat canopy your going for with plenty of large buds. If you are concerned about her height and size you can always do some HST like topping or fimming and some selective defoliation these techniques can maximize symmetrical growth createing a nice flat canopy with even light distribution. anyway great look plant and wishing you the best of luck for the remaining time left on the cycle :) Keep it green