People start smoking at different ages and for different reasons and for anyone who is a long term smoker it must be a hard thing to give up.
In terms of exercise smoking can have a very negative effect on your general health and fitness levels and make it harder to achieve any goals you might have.
There are stories of 50 to 70 year olds smoking 20 cigarettes a day since they were 16 years old and still being able to run a whole marathon. They are the lucky few who have a naturally high genetic level of fitness which the smoking has not affected too much. For other heavy smokers they might cough and struggle to run 1 mile let alone 26. The main thing to consider is how much easier or how much faster they could they have run the marathon if they hadn’t smoked all their lives and also how much faster their recovery time would be, I think in all these areas the results would have been much better.
The damage and long term illnesses from smoking have been highlighted extensively in the media and there are now various treatments and support agencies to help people cut down and quit all together.
The NHS has a very good website with lots of information, tips and advice http://smokefree.nhs.uk/