I hear you. Strange I thought it was like masturbation until I was like 17 or 18. I thought all guys had tried it and did it occasionally. Then I was told by several friends that they thought I was double jointed or something. LOL
All the more reason for more guys to also do more aerobic activity over weight training. As we get older our muscles become tighter. Weights increase the tightness. Where as aerobic activity with proper stretching has been shown to increase flexibility. Just avoid ballistic stretching techniques or bouncing stretches. That will tear muscles. Also, excess stomach girth will inhibit self-sucking.