Have ever heard anything so Daft, that so long as you quit by time you reach 30 you will live as long as a normal Person. It's a bit like saying it's okay to keep spinning the revolver chamber and pulling the trigger as long as you stop before the Gun goes off, I think it's called Russian Roulette. It’s setting a Precedent that it’s ok to continue killing themselves until they reach 30
As someone who did smoke from an early age (Capstan Full Strength)until I was about 35 years old it does seem to be true. After what I call a touch of Murphy's Law when all I seemed to have were chest problems after stopping, my health did really improve as was hopefully expected. I don't need my inhalers any more but I still keep my blue one handy for any emergencies. I can still do over 20 miles daily on the gym's X trainer so all I can say is that it worked for me.