I been doing since I was 8 yr old. I probably sucked me a million times. I had my gfriend suck it with me. She was amazed and always talks about it.
Flexibility, well maybe. Mostly, the technique. Warming up is essential. Jumping jacks, and sit ups precede a continued stretch towards it. Release, then stretch towards it again. Grab your arms around your thighs. Pulling as much as you can, then release and lay back. Repeat as needed.

I have had a wonderful experience sucking myself all my life.
Started at 8. Did a lot while 12 and 13. Chased girls for a while and forgot about me.
Started again while in a patch of "No Girl" at the age of 19. I was very glad to be back.
I had a great girl that loved Mr. Fatty. We fucked and 69 many many times.
I said I would like to lick her Clitoris while fucking. She said "Yea, do it."
We did it often. You talk about extreme HOT. WOW! I love to d that.
She had an enormous Clitoris, about a 7. I sucked that many many times.
She was my very favorite girl. Our first time to be licked while being fucked, she said, "WOW! You are flexible." Then, she never said another intelligible word. And she made high pitched sounds, which added to my excitement.
I'm just saying, Lick and Fuck is the best.

I love the feel of it, and the seeing someone else perform. The pics here give us an idea of how it looks from a more objective angle.

My load tastes really good too, so I never hold back.