Well technically, I think my POIS started way back when I was 13 and first started masturbating! I just developed an instinctual feeling that if I would abstain from masturbating, I would be mentally sharper, and generally on better form. But it was very mild, and didn't interfere with my life at all.
The symptoms only got debilitating once the testicular atrophy started... basically, the same stuff I knew happened when I was 13, just amplified to a huge degree. Then depression, lack of motivation, and memory loss came in later.