I.m 66, have reasonable at-rest heart rate, a bit above average cholesterol, a few pounds more-than-I-want-to-be overweight and do ~50 mi/week on a mtb...no serious hill climbing, tho....primarily cardio. I save my stress moments for Sat. mornings when I go do good hill hikes, i.e. this past Sat. I did 1000+ ft. elevation gain and a distance of 12-13 miles among the redwoods. Also dodged a bunch of mosquitoes during the jaunt.
My dad died @ 86 due to renal issues (prob'ly form the smoking he did most of his life) and my mom's still alive @ 90. No real heart issues in my family. I figure if I go while on my bike or in the forest, I should have a smile on my face (along with a bunch of scrapes and scratches if it happens while I'm on my bike).