Being an adult didn't used to mean low energy and the inability to enjoy life. That's what you get when you stop living and eating like God intended.
I played a lot of sports and did a ton of active things as a kid. Yet I couldn't work as hard and as long as my dad. He smoked like a chimney and drank like a fish, yet I couldn't keep up with him still.
So, if you don't have energy as an adult, it's your fault. You know you can make changes. You're just not willing to right now.
No excuses!