person A: I'm really said. I'm missing my youthful vigor. 
person B: Your youthful vigor? You think you're too old now? You're only too old if you allow yourself to be. My girlfriend's 90-year-old grandfather was a full-of-life WWII vet who lit up the room when he came in. Of course_comma_ you're not as physically active_comma_ but you have to learn to utilize your life in different ways.
person A: Yeah_comma_ I just don't have the energy I need to do things I want to. 
person B: Well_comma_ maybe it's an opportunity for introspection. For you to take time out of your day to think about what you need and want_comma_ and what are the best ways to achieve that. Maybe you need a better diet_comma_ or sleep schedule_comma_ or meditation_comma_ or an exercise routine. Sometimes you have to spend energy to feel energized. It's a slow process in the beginning_comma_ but it can be life-changing.