A few things to consider:-
1) As the years pass, the suspensory ligament (runs between the underside of the pubic bone to the supporting tissue at the top of the penis) tends to get stretched, so the angle approaches more towards the horizontal (or lower) This ligament is often cut in cosmetic surgery to make the flaccid penis hang lower, and thus look longer.
2) The weight of the erect penis can be considerable.
3) Treatment with anti-hypertensive drugs can cause a degree of erectile dysfunction - after all, it is all down to hydraulics in the end!