That is partly assumable - especially since more people are smokers than ever before. However, our average lifespans have also dramatically increased in the mid 20th century mostly due to increased hygiene and antibiotics: 18th & 19th c. around 35 y, early 20th c. up to 45 y, late 20 th c. going up to 65 y. (worldwide). And lung cancer regularly shows rather late (beyond 45 y, definitely).
For what it's worth, a huge portion of the increase in lifespan has been at the child-mortality end. If an average lifespan of 35 sounds low it's because a substantial proportion of children died before the age of five.
