Dude I have been running for years. Some months I do 4 to 5 days a week and others only 3. I do 5ks and 10ks and would like to do a half marathon. I have stated biking a few days a week. While I time has improved it is hell for me to get under a 15 min mile consistently. It hurts when I start and I am hurting when I finish. Yes I smoked for about 20 years and I have been quit for a long time. I am 63 and I feel like this is as good as I am going to get. But you know what? I am going to keep going because if I don’t I will get fat and die. So keep pushing.