All kidding aside, ride however you want but I have learned that it takes a while for knee to heal at any age.
My younger bro gave me a set of these (see link) they fit well under the jeans, the cost is about $60.00 I never go out without them.
ICON, Field Armour fits well under pants.
http://www.amazon.com/GUARD-FIELD-ARMOR-LEG-BLK/dp/B000WPKG70