In my younger days (I can't believe I'm saying that) I could go 2, 3, 4 times in an hour.  Obviously the latter is pushing it, but when the vibe was there I could do it.  I would often read reviews of providers and the client would say "I'm a one and done guy now, so...." etc.  I am 35 years old, but recently I've been just that, after I initially cum I don't feel the urge or need to "go again."  I feel my hobbying may be coming to an end.  This question is mostly for the men who participate in this hobby or just life in general, but I welcome providers insight as to how age differences and performance levels vary.

diet and overall fitness play a big part...the body's ability to have blood properly flow throughout is important obviously.
Testosterone treatment is very popular these days also, you have seen the commercials for the underarm stuff, but I know it can also be delivered to the body in other ways.  It's worth talking to your doctor about.  Might be something you can do.

If cumming several times in an hour is important, then looks like you are in decline and that really sucks!

It varies by person but recovery for a second pop can take longer. I can get two at times and other times only one.

I'm 37 now and for the most part I'm good with just once. Every once in a while I'll just keep going so I know it's still in there. I think the biggest factor is that as I have gotten older I have come to appreciate quality over quantity. I really enjoy just taking my time and thoroughly enjoying the ladies I'm with for the entire time (which can sometimes last most of the session). I have noticed with recently getting in better shape my stamina has greatly increased. Now if you can't last more than a few minutes and then can't get going again that might be an issue. If that's the case then try to pace yourself a little. It's always more satisfying to complete the marathon instead of just the 100 yard dash.

...having just recovered from an extended period if health related impotence...

Granted I recovered faster in my twenties, but I couldn't last anywhere near as long as when I was in my 40s.

The peak remained in place till my mid-40s, then I noticed a precipitous decline, especially by my mid-50s.

I almost never try to fuck after my second bottle of tequila, that never used to be a deal breaker until recently. After one bottle I can still fuck, but rarely cum. Alas, the concessions we make to get our dicks wet in our old age. lol

Wow! You are a sex machine. 4~6 times a day with multiple dates, can't afford the time!

but nothing like only a few short years ago. I no longer have any desire to see four women in a single day, although I will confess, there are days when on vacation that I will see three.  The mind is willing, but the body just isn't interested in having that much sex anymore. I know the day will come when I won't even want it everyday, but I hope that day is decades in the future.

At your age, you are still a machine. I hope I can even do half of what you can do. Don't worry about lose interest. If you lose the desire, you lose nothing, unless you have nothing else to do in your life.

Most of us have been where you are.  But, as with many aspects of life, one learns to compensate for the impacts of age.

Don't sweat it....as most have already said....savoring, being creative, attentive, and taking your time will be even more enjoyable.

Because like AC/DC says, you're already there

I do love sex with the right partner, HOWEVER, I am not and never been into marathon sex. 20 minutes for us both and I am done, satisfied and ready to do something else.  

I've found that, unfortunately, as I've gotten older, I got a lot more winded and tired afterward. Last year, there was a period where I exercised a lot and got in real good shape for me. Got rid of the spare tire and felt great. And I noticed the sex drive came right back again. I could go all night. Now that I've gotten out of shape again, I'm right back to being "one and done."

No two bodies change the same way. There is no "normal."  Get a thorough physical to make sure nothing else is going on. If that's clear get your self some viagra!

I once saw a lady who spoke of an 80 something client who could pop 5 times during the hour session. So I'm pretty sure it's different for every guy. As for me, the decline started in my forties, then dropped off a little each year. That being said, there's also a roller coaster aspect to the decline. There are moments of brilliance, but those become less and less with each passing year. Now that you've noticed your own decline, you get to start the game of finding the right magic potion.

I have done more than one in an hour but the 2nd for me just was not that enjoyable.
More like work!

We were raised in a society where sex is copulatory only, ideally between a female and a male and it ends with male orgasm. What the fuck? we are conditioned so bad to this belief that we measure our sex skills purely on erection and ejaculation. Well, that is just not true and now you have to work on breaking the mold you have been living unaware trapped in. This actually represents an opportunity to reframe what is intimacy, companionship, foreplay, afterplay (hell, I had amazing sex in second rounds I never to got to end). The purpose of sex is not to come; the purpose if to get aroused, connect and share that closeness to lift your mind, body and soul. I highly suggest you read The Erotic Mind by Jack Morin, a must read; and maybe take a look at Chris Donaghue's Sex Outisde the Lines which points at different points how ignorant and oblivious of it we are.  
Do not take my answer as criticism, rather as some advice; for me reading these books and becoming interested in the topic and looking at shaking up the constraining accepted idea of how sex should be has been tremendously enlightening. You may find that you enjoy sex in years to come much more than you did in the past.

I'm 28 and have always been a once and done guy.  Even in my sexual peak of around 20yrs old.  In rare cases I can do twice but never more than that.  I usually need until the next morning to recover, and really don't feel the need to be relieved again until a few days later.  My ideal frequency of sex would be about once every 3 days, minimum is once per 7 days, after that it starts getting uncomfortable.