Here is my history along with the others.
HS - the wimpy kid. Could not put on weight while eating all that I wanted. Below average racing results with running and cycling. A pity letter my senior year. Running or cycling about an hour a day.
College - kept cycling. Could not put on muscle mass nor was ever strong in the hills or sprints. Slowly getting better as it was harder for people to drop me in a race. Cycling anywhere from an hour to four hours a day.
After college, married - back to running. Worked up to an hour a day and would do 10Ks under 40. Started with Lydiard training and would run two hours a day. Never lifted, just ran. Times dropped and I was usually in the top ten at races and won some smaller races. Marathon best of 2:32:30. 5K best of 15:30.
At age 40, with 5 kids - just kept training with no real racing goals. The running was falling apart and found it hard to run three days in a row without extreme fatigue and muscle soreness.
At age 55, with kids gone - started lifting weights because I could not run or ride every day. Lift for an hour on my easy day and swim because I felt tired from the day before. If I wasn't lifting and swimming as a break, I would feel perpetually tired trying to run and ride two hours or more a day.
Now over 60 - training like a triathlete routine (don't race) along with weightlifting keeps me sane, muscular and healthy. More cut than ever with six pack abs and my youngest son says that I look like an assassin.
My summary advice is while you can run - RUN. My running times would never have been as good if I was taking an hour away from my two hour a day routine. When I could no longer run two hours a day without breaking down, I diversified to continue with a two-three hour a day workout. Still can eat all that I want.