Maybe find some low profile knee braces to ride in?
The other thing that is kind of obvious is to ride within your abilities, especially when it comes to speed.
Everyone, old and young alike, fall into this trap as gravity sucks them down the hill and going fast is so much fun. Its like the advice on all the park signs "look before you leap" and "easy style it".
Finally, what we do is inherently risky, probably more so than your "contact" sports. The only thing you can do to change or mitigate that is to not participate.
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