At 65, I joined one of those fitness centers that does organized workouts with a coach. It was a great move, not because it motivated me to workout, but because the trainer taught me how to do the moves correctly. I moved on from that gym and now I use Jeff Cavaliere's Athlean X Youtube channel when I want to know the proper form for an exercise, but it's not as good as having a trainer who can spot your mistakes. Fortunately, I have a training partner who spots for me and points out little mistakes. Now at 78, I hit the gym... Planet Fitness or Gold's Gym... twice a week.
Thirteen years ago, my running friends asked, "Does it make you faster?" I responded, "I'm not lifting to be a faster runner next week or next month. I'm lifting to be a better runner 5 years from now!" So far, that has worked for me.
I'm not a distance runner. I stay under 20 mpw... typically around 12-15. For all its benefits, distance training has some downsides: It constantly floods the body with cortisol, which in turn suppresses the immune system. It lowers testosterone levels, which decrease by up to 90% with age. With SIIT training and several sets of various lifts to exhaustion every week, I'm typically between 550 and 730 in my annual testosterone checks. If you're a distance runner over 60 with a T level below 300, you would probably benefit health-wise by considering T supplementation.
Weightlifting boosts testosterone naturally.
Other than dumbbells, I don't use free weights. I lift to exhaustion on some sets and it's safer to do that on a cable machine than with free weights. Most of my leg exercises are single leg: skater squats, Bulgarian squats, etc.