I live in the Great White North and got into running and biking as off season training for cross country skiing. It wasn't until I started spending time with hardcore triathletes that I got serious about them however, Marathons, Ironmans and Century races followed. That was in the 1990's, I was in my 40's. I'll be 70 next month.
I think all endurance sports are addictive (endorphins) but yes running is hardest on the body. It also gives you the fastest access to those endorphins. The only way to get an experienced runner to quit is through injury, even then it usually takes several. Many people get injured when they first take up running, too much too soon. Others carry on until their joints start to fail, too much for too long.
Where do I fit in this, well I'm still doing Olympic distance triathlons. I can only run because of some well known super cushioned running shoes. I'm 40% slower on the bike and run than in my 40's and 20% slower on the swim but hey, I'm still doing it. I'm only doing one long slow run, 20-30k, and one long ride,50-60k, a month. The rest of the time I do
High-intensity interval training , specifically the Vollaard regimen. We'll see how it goes in the future but for now I'm still enjoying training and the after race comradarie (parties). I do wish I had started the HIIT type training earlier, like maybe 10 years ago. It might have saved me pain and injury downtime, but who knew?