I have every respect for elderly pilots who still smoke(provided that it is nowhere near me). Many of them started when the jury was still out on the subject of whether or not it was harmful to the body.
It is, I believe, easier to give up heroin than nicotine. So I can well understand their inability to quit.
I have no patience, tolerance or understanding of some young man of your age who is allowing himself to get dragged into the addiction, when the medical evidence of it causing harm to yourself and those around you is undeniable and has been around since before your birth. Virtually every UK company has banned smoking on the flight deck and in the offices, classrooms, simulator buildings and crewrooms.
Just one reason for you not to smoke: At 6000 foot cabin altitude, the carbon monoxide in your drug will combine with the oxygen carrying part of your blood with far greater ease than oxygen will. ie it partially blocks oxygen uptake leaving you effectively at a higher cabin altitude than your non-druggie friends.
I have sat watching a fellow pilot die from a heart attack at the age of 47. He was a heavy smoker, convinced that it was doing him no harm. Since then I have been a little anti-smoking!
I will now keep my head down to avoid the flack from the druggies who can't quit and have to try to justify their habit!