That's awesome, thanks! Having never been in great aerobic shape (but having a basis of athletics in soccer and some medium distance cycling in my youth, in my late 40s I started training and at 50 began triathlon as a way to build up a deep aerobic base. Along the way I discovered that contrary to earlier research it's possible to train for optimal fat burning, not unlike the way one can train for maximum glycogen storage (earlier studies had missed this because it takes a minimum of 6 weeks to start seeing effect.
I know it worked for me because I found that if I biked to a blood test, even if it was only 15 minutes of riding I would have high triglyceride levels to the point my Dr was complaining. When I took the bus to my blood test the tri-g numbers were rock-bottom. So while conventional wisdom says fat burn doesn't begin until 30-45 minutes into a workout, I'm quite certain that the training worked.
This btw was all a decade before I started HRT, yes training matters as does innate ability.