Leonardo DiCaprio: Good Genes or Good Docs?

Leonardo DiCaprio isn’t showing any signs of growing pains!

Here’s a 19-year-old version of the talented young actor at the premiere of his breakout film, “What’s Eating Gilbert Grape” back in 1993 (left) and 23 years later ... the climate change buff -- who celebrated his 42nd birthday this week -- at a fancy schmancy Hollywood party earlier this month (right).

Never let go.

The question is ...