It doesn't hurt to mention it at times. Sometimes it takes a while to sink in. I'm probably not the only person who heard stuff like:
Youth is wasted on the young, Time flies, etc. and didn't pay close attention and now I'm nearing retirement I understand what the "old" people meant and regret I wasted so much of my youth worrying about trivial stuff like the typical "what if she says no?". Or not spending more time with the parents, etc.

As a teenage I recall my uncle, now 81, tell a story about his coworkers. He said most of them made solid money but all seemed to live from paycheck to paycheck. He then realized they were all "house poor". They had to have the best house they could afford (or maybe couldn't afford). While after my first house I always tried to get into good neighborhoods, I usually had the lower end house of the neighborhood with multiple fixer uppers. All I could afford on a single income government paycheck. I did always avoid debt except for house and low interest car loans. Somewhere along the line I either heard or thought of the expression "Money can buy you possessions or freedom" and I preferred the freedom.

So keep talking with the kids, just not in a pushy manner and something might sink into their brains.