Biologically it's not double, you need to add 9 months to both. Then it's not 12m vs 22m, it's 21m vs 31m. Still a big difference but not twice as fast, just 48

Biologically it's not double, you need to add 9 months to both. Then it's not 12m vs 22m, it's 21m vs 31m. Still a big difference but not twice as fast, just 48% faster overall. Brain development starts very soon after conception.