Here you go:
1) Get some good porn;
2) Watch porn with keen interest;
3) Lube the palm of the hand you use to JO with but not the other one;
4) Form said hand into a fist, but not so tightly that you cannot easily insert your cock;
5) Begin pumping your cock into the lubed hand;
6) As the point of no return begins, aim the head of your dick into the hand without lube on it;
7) Ejaculate into the palm of the unlubed hand;
8) Lick the fresh ejaculate from your unlubed hand, beginning at the palm, next the fingers, then finally the wrist (should there be any there);
9) Swallow after taking a moment to enjoy the taste and texture;
10) For the sake of preparedness, have a glass of something tasty nearby: if you don't like the taste of your ejaculate, this should act as a palate cleanser.
I hope this step-by-step guide helps you through this obviously complex procedure. It takes time and effort to become really proficient at eating one's own cum. Do not judge yourself too harshly should your initial efforts not meet with 100% success and remember: practice makes perfect.
This guide can be used by all men who prefer to not mix acrobatics with their masturbation, whether because of age or weight issues. It also prevents the possibility of potentially painful cum in the eye, which makes it win/win.
As to increasing the longevity of orgasm, try and redirect at least some of your masturbation away from your penis. Some guys (like me) enjoy titplay, others prefer some prostate/anal stimulation, most men enjoy some attention paid to their perineum.