The Messenger of Allaah (peace be upon him) is reported to have said , “There are two blessings which many people waste. They are good health and free time”
After having treaded so far you *learn* and understand. At this point in life, the most significant thing is good health. You understand it too late - the importance of time and health. As healthy and energetic you were in your twenties, you are not in your thirties and would be definitely weaker in your 40s and 50s - if you are to live, of course.
The worst realisation for a person would be to look back and see that s/he has wasted a very important and stronger portion of his life doing things which would not be of any use to him after he has travelled his entire life span here. That is, he has so far headed towards his eternal abode with no preparation and no savings for his eternal comforts. Knowing a thing and implementing the knowledge are two different things. The difference between these too would matter the most when you realise that certain implementations could have been the ultimate investments for your Aakhirah!
May Allaah guide us towards actions that do not become a cause of regret when we are placed alone in the dark, under the ground. May He forgive us for all our known and unknown shortcomings and guide us towards the best utilisation of our time and health and help us to understand that the true purpose of our lives is in pleasing Him and beautifying our eternal abodes with Him (Ameen)