I don't think high kicking results in injury, I think bad training does. By that I mean if you are setting realistic physical goals, then you train into the kick not attempt to kick higher than your body allows, not matter what age you might be.
Of course the older you get, the more you may need to moderate what you can aspire to do. But training you body to be more flexible is not in and of itself a bad thing, in fact quite the contrary. Flexibility prevents injury and should be a key element of any fitness regime.
That does not mean you need to be able to to the Chinese splits, but you should work within your bodies limits to do what you can.
Being able to kick high, doesn't mean you have to actually kick high either. The flexibility will make your mid and low level kicks even better because you are not fighting against tension and working well within your full range of motion. Plus in many situations high kicks can be very effective. Especially sporting but I wouldn't limit it to that.
We've seen in the UFC what a head kick can do. Personally I can kick to the head but rarely do, and most people I spar don't know I can. I've scored some really night head kicks because opponents defend thinking I will never go upstairs.
In self defense, I agree not generally a first option for many reasons. But never say never. Fighting is ugly and messy, you just might find your self out of range and your attacker set up for a solid kick in the head. Stranger things have happened.
Undefeated in all of Asia!