1 oz of gold is ~$1800 USD atm. An average not-overweight adult is, say, 70 kg (~150 lbs). That’s approx 2500 oz.
2500 oz of gold is worth approx $4.5m USD. Over a 20 year career, income of $225,000 / yr accumulates to $4.5m.
I guess that 20 yrs and $225k are low-balls, too, for good programmers – atm at least. Or they might retire early.
Either way, the idea that the lifetime work of a programmer is approx worth their weight in gold is pretty close (at least atm).