Now that I am older, my back gives me problems.  I have found most of the time I have the lady screw me Cowgirl.  

Absolutely.  Cowgirl is my favorite especially if she knows how to ride. Yippee Ki Yay, motherfucker.

is whatever the lady likes best. The more she’s enjoying herself, the more fun for me. I love all positions—CG, ACG, RCG, doggie, mish, coital alignment mish, lazy dog are great.  About the only one I can’t do anymore is upstanding citizen, unless the lady is very petite as in 100–110 pounds or so.

Missionary is a lot of work, but it is still the best overal position.
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For some reason doggie doesn't keep me erect.
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Cowgirl is pleasant but never stimulating enough for me to O.
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If I'm pooped out and haven't O'd yet, either a hand job or oral will usually be my "let them do it" while I lay on my back and relax.

I enjoy all the CG positions, Rear, Asian, Rear - out of the saddle (between my legs), but it has nothing to do with being tired, pain or any problems!
I keep pretty fit, so I can be able to enjoy the whole session!

so they want to lay on their backs as well.

So Doggy.

Two slipped discs operations over the years make me careful on sex positions. Cowgirl is safe and it can be hot if the provider is ok with kissing. Even if things finish up with hand or oral, its still a great day.  

My preference as well, particularly if they know what they're doing and are good at it.  The 'grinders' are the best!

My lover has a bad back he was in a car accident, so this works best plus I get thigh exercise with the added bonus of controlling how it hits my G-Spot. I don’t mind putting in the work. Lol Smile for me!

I spent 20 plus years in a marriage with no oral OR Cowgirl.

..... Fortunately, I have no limitations.  I like to box the compass, standing up, sitting down, on my back, her back, on all the furniture, in the sex swing, in the hot tub, on the boat, etc. etc. etc.