I htink your nerves are getting weaker which happens when you get older if you aren't keeping them strong. You should do some resistance train along with aerobics like Hippie Dickie stated to keep you nerves strong and have endurance.
Also, I have a theory that people become addicted to tobacco because they have low niacin levels and nicotine helps keep their levels better than they normally are and this is what keeps them smoking even though they know they should slow down or stop. You see nicotine is very similar to niacin a.k.a. Vitamin B3 or nicotinic acid and it's water soluble meaning it isn't stored in the body and you can only get it from certain foods and you have to eat it daily. Your body can make it from tryptophan BUT that is only done when you have iron, b6 and b1 present.
I think when you smoke your body is recognizing the tobacco as a source of niacin but the way you are doing it is making it dangerous to your health(smoking) not the actual tobacco unless you are smoking/vaping low quality brands that have tons of chemicals added to enhance the affects. American spirits is a good brand to buy without all the added nonsense.
I think you should also eat more foods that have a good amount of b3 in them along with foods high in the other vitamins and in a good ratio to keep everything balanced and to lower your rate of taking tobacco. I know for me I don't need that much tobacco and can stop whenever I feel like it and I think my diet is the reason. I have went weeks of puffing and stopped when I didn't feel like it, gave the rest of my pack to someone else and didn't have any withdrawal symptoms. Try it out plus the exercises and it may help you.
EDIT: I forgot to mention you should eat more soluble fiber so you can grow a good amount of friendly bacteria that help make niacin to be used by your body and keep the levels good.
Another thing I just realized, adding a little tobacco with cannabis could be why it keeps me from getting lethargic and keeps the high come down nice. The nicotine is acting as niacin and helping my nerves process the thc and other oils which are attached to the fatty parts of my cells. Remember niacin helps process fats!.
niacin-B3
http://www.whfoods.com/genpage.php?tname=nutrient&dbid=83