I wasted my 20's and got diagnosed with cancer at 30. It changed my perspective quite a bit and so far my 30's have been the best time of my life.
It was the initial stage where I felt I had a death sentence that shifted my outlook on life. When you think you're going to die you re-evaluate some things. I looked at my life, thought about what I'd regret, and made 5 year plans to get things on track. I'm now in the habit of setting plans for 5 years to ensure I don't regret the life I do have.