30 years ago: Spend more time with Grandpa
20 years ago: Enjoy school more, you won't get that time back.
10 years ago: Quit recreationally using tobacco before you get addicted. (I eventually did get addicted, but have quit for a few years now) Also, you're in a recession, buy a smaller house with less payments.
3 years ago (bonus round): Finish building your hotrod already, it's not gonna get done if you don't do it now! (it's still motionless in the garage, and the toddler gets all my free time now)