Olympic glory is for the young. Gymnast Gabby Douglas is just 16 years old, swimmer Katie Ledecky is only 15, and Michael Phelps, age 27, says he's old enough to make these Olympic Games his last.

But the Christian "race" is for young and old. The fight of faith is for the healthiest and sickliest, for the seemingly strong and the weak.

So how is it that an aging Christian — barely able to walk, much less compete in Olympic track and field — can have the wherewithal to run?

John Piper tackles the question:

The answer is that we all must run, whether old or young and whether sick or healthy. And this is possible for the sick and senile because the race is a race against unbelief not against sickness or senility. It is possible for the unhealthy to win the fight because the fight is a fight against lost hope, not against lost health.

Here’s the biblical proof for this. In 1 Timothy 6:12 Paul says to Timothy: “Fight the good fight of faith; take hold of eternal life to which you were called when you made the good confession.” So the fight is a “fight of faith.” It is not a fight to get out of bed, but to rest in God.

It is not a fight to keep all the powers of youth, but to trust in the power of God. The race is run against temptations that would make us doubt God’s goodness and love for us. It is a fight to stay satisfied in God through broken hips and lost sight and failed memory. The race can and may be run flat on your back.

Again Paul said in 2 Timothy 4:7, “I have fought the good fight, I have finished the race, I have kept the faith.” Finishing the race means keeping faith. It is a race against unbelief, not against aging.

Another way to put it is that the fight is a fight to keep hoping in God. “[Christ] will present you holy and blameless and irreproachable before [God] provided that you continue in the faith, stable and steadfast, not shifting from the hope of the gospel.” Finishing the race means not giving up the hope of the gospel. It is a race against hopelessness, not against flawlessness.

When we cheer on the diseased or aging runners who run their final laps in hospital beds, what we are really saying is, “Do not throw away your confidence which has great reward” (Hebrews 10:35). The finishing line is crossed in the end, not by a burst of human energy, but by collapsing into the arms of God.

And don’t forget. In the Christian race, we do not finish alone. We finish together. It is part of the rules (Hebrews 3:13). We restore the straying (Galatians 6:1; James 5:20). We encourage the fainthearted and help the weak (1 Thessalonians 5:14). We stir each other up (Hebrews 10:24). We “visit the widows in their affliction” (James 1:27). 

The above is from Piper's 1992 article "How Can Elsie Run?"