I'm 56 and have always been pretty active & fit. However, I joke that I have to work out twice as hard and eat half as much just to stay lean at my age.
My bodyfat (measured by a combination of calipers and digital measuring tape) is consistently between 12-13%. I have "sorta" visible abs. Every POT I've encountered has said I'm pretty fit, especially for my age.
So here's my training regimen:
1. Push-Pull-Legs (resistance training) 3 days per week. Compound movements primarily (e.g. bench press, deadlift)...If I have gas in the tank after the compound movements I'll do isolation exercises (e.g., bicep curls).
2. HIIT 3 days per week. Always on a Wahoo Kickr (an erg machine I attach my road bike to and I use a training platform to automatically adjust resistance during the interval workout). These are usually 30-45 minutes and I'm spent at the end. This is a GAME CHANGER for stamina.
3. Yoga/Core usually on HIIT days
4. 20-30 minute walk after dinner each night.
I also supplement with testosterone. I work with my MD where we monitor hormone levels 3-4 times per year. We make sure my free and total testosterone is at the upper limit of "normal" for my age and weight. So I'm not some vein-bulging roided-out looking dude. Just someone who you would see on the street and say "he's fit for his age."
If I had to choose between TRT or workouts out I'd drop the TRT and just focus on a good diet, compound movements, and intense doses of HIIT cardio.
Between the HIIT and strength training I have no problem in the bedroom with my stamina or ability to pick up my partner and move her around (if she's submissive and likes it).