There's no account for planning! If common sense was in gear a job(paving or roofing) like that just wouldn't occur in summer months. Sadly, common sense and timing get mix matched all the time. The last 3 roofs I've built occurred in the summer months. Tar paper so hot your boots would just push up little piles of tar as you slowly tried to slide off the roof.
I honestly think age is all in your head. I mean obviously there's some factors that will play into things but staying active I think is a good part in it. Keep it up!