Questions from a novice

I have been doing Jelq and stretching for six months and I have gain one inch in flaccid length an 0.5 inch in erect length.

I have three main questions I would like to make to the community:

1- When do you know your penis will not grow anymore? Is there any physical signs that can show that no matter how much training you put, you will not grow more?

2- Is there any way you can increase the resistance of your penis to workouts? I feel I can’t workout for much time.. I can’t jelq for 5 mins straight.. Is there anyway to solve the problem?

3- Is there anyway to minimize the effects of turtling or to predict when it will happen?

I also would like to know if it is normal for my penis to be hurting on the tip after one session of intense jelqing two weeks ago? I have been resting since then, but it still hurts.

Thank you in advance