It certainly is!
It's never too late - even the very old benefit.
But the sooner the better - the less risk of getting an incurable disease. Without a daily dose of poisons, health starts to improve immediately.

• The pulse rate returns to normal within 20 minutes of quitting.
• In the next two days, toxic chemicals such as nicotine and carbon monoxide are expelled from the body.
• Blood circulates better.
• Within a few months, lung capacity grows, and coughs clear up.

If a young person quits, soon there's no difference between the health of an ex-smoker and a never-smoker.