When we are children, waiting for a birthday or Christmas or other anticipated event takes FOREVER. Each day drags on, and a whole month seems like an impossible distance across the abyss.
Now a month passes between blinks, and birthdays come much faster than I can mentally process them.
I've figured out why. When we're children, each year is a bigger percentage of our entire life, but as we add years, each one becomes a smaller and smaller percentage and so seems to pass more quickly.
The oldest living thing is the bristlecone pine pictured above, which by its rings is over 5,000 years old. That venerable tree has seen quite a lot of history come and go.
In contrast the mayfly in its adult form lives less than 24 hours. Its only purpose is to reproduce. But if you could ask a mayfly if it felt cheated compared with the bristlecone pine, I doubt that it would care. From its perspective a successful life means completion of its purpose.
Even though they didn't live their full "threescore and ten" these people managed to accomplish a lot in their short lives. The number of years is not what's important. As Gandalf says in J. R. R. Tolkien's Lord of the Rings, "All we have to decide is what to do with the time that is given us."
Or as Paul wrote about 2,000 years ago, "Look carefully then how you walk, not as unwise but as wise, making the best use of the time, because the days are evil." (Ephesians 5:15-16)
Time is our most valuable commodity. Einstein was right--it is relative, and relatively speaking, shouldn't we make the most of what time we have remaining?