The only thing wrong with pulling your pudding at 13, especially twice a day, is you may develop the one bollock stretch syndrome. This is a condition that many grown men suffer from, due to excessive wanking. You see the two bollocks tend to be the same length before you begin to pull your pud. Following two wanks a day from the age of thirteen for two years, causes you right bollock to sag while you left bollock begging to retract into the sack, and of course you suffer later on in life, because instead of cumming, you have a tendency of going, as your right sags and left nut begins to crack under pressure from the two handed jerk. So you must be careful. If you notice that your right nut is lower than your left, then that is the sign of getting a dose of nut cracker syndrome. Be careful that you do not find that your cum, does not come out but goes in. If this happens, stop jerking off for a month or so. This will allow your wrist to also get better and your nuts to reestablish normal growth.