Complex sentence: He was a non-smoker for most of his adult life, but smoked heavily in his youth (25 to 40 cigarettes a day); he eventually quit, calling the habit "a waste of money".
Split into simpler sentences: He was a non-smoker for most of his adult life, but smoked heavily in his youth (25 to 40 cigarettes a day). He eventually quit, calling the habit "a waste of money".