I guess I just don't relate to the women I meet in any like manner to my daughter, so the comparison never crosses my mind.

On the other hand, I don't tend to see too many young women, so it doesn't come up very often.  I have one gal I see who looks like a teen (petite Asian) but is around 30 now, but that's not far from my daughter's age.

I can't think of any particular litmus tests I have for the providers I see, other than they aren't working for LE at the time I see them

Anyway my thoughts on the age of the provider is in the link I included below.

Any female under 21 is simply too young. I couldn't have sex with her. I couldn't even spend time with the few 18, 19, 20 yr old strippers I knew and I was 20 years younger then.

As my daughter ages, so do the ladies I choose. They still look younger to me as I age.  

I couldn't imagine banging some 20-yo. I probably could if they promised not to talk.

I see hookers younger than my Granddaughters and it doesn't bother me a bit. They have chosen this line of work. I'm just helping them out.  
But still prefer the 40 year olds.

...I've got a hangup about seeing women where I may be as old or even older than their Dad!  Needless to say, my field seems to be narrowing every year...

daughter is over 40 if I had a rule like that my options would be limited.  I actually almost never think about that aspect of seeing ladies.  And every once in a while I run across an under 25 hottie who I just can't pass up.  And yes, most of the time there is little in common intellectually, but a while back I had a great time repeatedly with a 23-year-old who could relate to me pretty well (and was extremely hot!).  So I think it's likely different strokes for different folks.

a woman's maturity, conversational compatibility, sexual experience, and ability to relate to an older guy and his desires and abilities.  Perhaps a particular 20 something lady could fit the bill, but I won't risk the hobby dollars to find out.  There are way too many mature provider choices out there.  And, in my opinion, the probability of a mature lady providing me a great time is much higher than that of a 20 something lady.  So I stick to mid 30s to mid 50s, with 40 to 50 being my most common choice.

When I reached 50, I decided to see providers who were at least one-half my age.  When I turned 60, I changed it to at least 2/3 my age.  I am now 73, so the minimum age is close to 50.

I won't see a provider who is using the same first name as my daughter.  

My daughter is 30 so ....

Generally I prefer over 25, but if they are college grads or close to it I will go younger.  I need to have something to talk to them about besides Justin Beiber.