I just found out I have polacystic kidney disease I'm 21 I'm just wondering do you get a kidney transplant when you reach end stage or before hand?

Nephrology. Timing of renal transplant is a discussion your nephrologist can easily answer. Your renal function will be followed closely and at some point it may become necessary to begin dialysis. As this time approaches discussion about transplant is appropriate. Transplants are not done "prophylactally" and there is no certainty you might require dialysis. Follow up regularly with your physician.