I am in my mid forties and ride a seven speed cruiser or maybe mountain bike. I enjoy pedaling while standing, and I don't really care about speed or efficiency. When there is even the slightest uphill grade and I stand. I get in a high gear and enjoy slowly swaying back and forth and using my arms. I've never really measured my cadence, but I'm sure it is sub 60.
I am putting some longer rides in reasonably hilly country with smooth roads. My knees don't ache afterward. Sometimes my shoulders ache a bit after the ride but doesn't feel damaging. I have been doing hills/grades in top gear as my own "check off the list" challenge.
If proper form (for standing at least) and in good shape, am I abusing my body/knees? Up to now they feel great, but I would hate to have "reality" crashing upon my knees someday.