If you’re not smart by 20, married by 30, or rich by 40, you won’t be.
David Graves told me this slogan many years ago, and the more I think about it, the more accurate I think it is.
We need milestones as we go through life. It helps if we know whether we are on track with our stewardship of time and capital. We know that we are bounded by age. Caleb gave us our actuarial guidelines: at age 85, he was still a strong man, which was abnormal (Josh. 14:10-11). Moses confirmed this age limit: covenant-keeping mankind on average gets 70 years of productivity; anything beyond this is pure gravy, statistically speaking (Ps 90:10). This is not a permanent biological limit, for Isaiah speaks of very long life spans as part of the era of millennial blessings (Isa. 65:17-20). But for today, we face these actuarial limits.
In Mosaic Israel, a man’s entry into adulthood and citizenship took place at age 20. This was the age at which he became eligible to serve in God’s holy army. When called into holy war, the nation’s military leaders numbered or mustered every man age 20 or older (Ex. 80:14). This was the definitive break with childhood. He who was unfit for military duty because of mental retardation would remain ineligible for life.
Smart by 20
A man’s level of intelligence is established mainly by genetics. He cannot escape these limits. He can learn more about new things, but meanwhile he forgets what he learned before. Wisdom comes with age; intelligence doesn’t. A retarded person is not expected to become intelligent through education or any other means. A very unintelligent person cannot experience new-found genius, although idiot savants do display abnormal abilities in narrowly defined areas, such as numerical computation or musical ability.
Intelligent people are not expected to be wise by age 20, but they are expected to know a great deal about their own ability to master new information or certain kinds of information. At age 20, a person is ready to plan for the future, for he knows his intellectual limits. He who plans to be a medical missionary had better have grades that will get him into medical school. If he does not, it is time to plan for another career.
If some skill does not come easily by age 20, it will probably never come easily. In some fields, the die is cast by age 20. Mathematics and theoretical physics are examples. If a man has not made a major mathematical breakthrough by the time he is 20, he probably will not make one. By age 35, a theoretical physicist is out of the running. He is no longer expected to make major breakthroughs.
(For the rest of my article, click the link.)