Donald -- you bring up some compelling questions. Here's how I view it...

The difference between race and gender identity (and age, to an extent) is that people of all skin colors across the spectrum basically copulate and fornicate in relatively the same way. So there's no functional reason why race would be an impediment when it comes to sexual pleasure.

On the other hand, for people who have had HRT or gender-reassignment surgery, sexual intercourse with a cisgender person simply won't work the same way it would when experienced between two cisgender people.

Some cisgender people can still attain pleasure if in sexual/romantic relationships with transgender people...but some of us cannot. Neither scenario is "good" or "bad." It just is. It depends on what arouses us (whether we're cisgender or transgender), sexually, as individuals.

Age is less clear-cut. People can be sexually attracted to someone who is many years older or many years younger than them. The potential problems can arise when either: A.) sexual intercourse/pleasure is hindered due to the physiological deterioration that can be experienced by people of ALL demographic groups as they age; or B.) the divergence in life experiences, when there's a significant age gap, might be psychologically insurmountable insofar sustaining a long-term relationship.

So age CAN be a deal-breaker, in terms of sexual pleasure -- but it isn't always. Gender identity can be a more frequent deal-breaker, even though, again, it isn't always. Race per se would rarely be a deal-breaker...and, if it is, then it usually has to do with the attitude/worldview of one's sexual partner rather than their skin color per se.