How long does it take to stop feeling the impact of cigarettes on your fitness?

I found this timeline:

https://www.medicalnewstoday.com/articles/317956.php

It seems like 9 months is the average for significantly improved lung function, but that's an average, for all you know for you it could be 13 months...

I think you will carry on improving.

There is a breathing trainer called PowerBreathe, I used to use one.

If breathing is a limiting factor, then you might want to try the Douillard, Buteyko, or Oxygen Advantage breathing method. Buteyko and McKeown (Oxygen Advantage) are similar and you can read about them online and watch videos on youtube. I have tried them briefly, but they didn't do much for me, probably because I've been doing the Douillard method for over 15 years.

John Douillard's method is different. It focuses on strengthening the diaphragm by forcefully breathing out through the nose as much as possible.

I learned the Douillard method from his book Body Mind and Sport, published in 2001. You can buy it used on Amazon for a couple of bucks. It has definitely been one of the factors in helping me become a world class age grouper in the 400 and 800.

Like other books, I'd take some of what Douillard says with a grain of salt, but the mechanics of breathing seem to be right. In a nutshell, it's this. Breathe out forcefully by contracting the diaphragm, making a Darth Vader sound, mostly breathing out through the nose. Allow air to flow back in naturally. Don't forcefully breathe in. The air will come in naturally as your diaphragm relaxes. It will take a few weeks to strengthen your diaphragm to handle the new method. It works best at fast paces. Doing it at slow paces will cause you to hyperventilate at first.

The nose can't handle all the volume at faster paces, but even a limited amount of air through the nose creates a lot of physiological effects that would take too long to describe, but the effects will improve your running performance, in my firsthand experience.

Oh, just to be clear, I haven't given the Buteyko and McKeown methods a fair trial yet. They both make some fascinating claims that should only take a few weeks of regular training to prove or disprove for your personal situation. I'm trying the McKeown method, but the only benefit I've found so far is that it has improved my ability to hold my breath.

Damn. Props to stopping while being young enough, def a habit you don't want a decade or 2 from now.

Somewhat scientific breakdown of your lungs, they're full of air pockets called cilia (any smoker knows this), and that's where the impact of smoking gets accumulated.

You started while young, but are young enough to reverse that potential damage. Aerobic exercise will be excellent to help alleviate the build up mucus. Look for foods that help decrease inflammation too. Continue running and stay away from the cigs, in time, you'll begin to feel the difference.

Just keep running. No more smoking. Don't drink if you do. By the time you're 26 you'll be able to run up a mountain while your peers who didn't give up smoking will be sitting at the bottom. Just keep running and you'll get all the wonderful benefits that last a lifetime.