Therefore we do not lose heart. Though outwardly we are wasting away, yet inwardly we are being renewed day by day. For our light and momentary troubles are achieving for us an eternal glory that far outweighs them all. (2 Corinthians 4:16-17)
Some days I feel like I have a negative balance on my energy. You know how it is, when your muscles ache, your eyes hurt, you're exhausted, and there's about 5 more days before you could possibly get more than 5 hours of consecutive sleep?
Well, today's verse isn't exactly saying that it's ok for us to waste away too soon. He can restore us to health and strength at any age. But when I read this what it says to me is yes, I'm getting older. And yes, some things are going to be harder to do or keep up with. I may not be able to pull all-nighters without feeling some very adverse effects, for example.
What I read, then, in this verse is that from the moment we are born our bodies begin the march towards death. But our mind, heart, spirit... those are things that are renewable, those are the parts of us that remain strong and true. We will eventually lose our physical health, but our spiritual health is what we must keep as our number one priority, for it is that health that will accompany us to Heaven. We will be given a new body.
Do not let this be an excuse to eat cupcakes for the rest of your life, because stewardship of your body is part of your responsibility in life, but do not lose heart when and if you lose some of the physical abilities you once had. If you are reaching towards the goal with your whole heart, mind, body and soul, then anything which tries to hold you back will be used instead for God's glory.