My hubby, the math person, offered to explain it to me. I declined.
He also pointed out that the 111 doesn't work for kids born in this century - theirs adds up to 11.
Grandson David - born 1999 - add 12 (age this year) = 111
Grandson Kyle - born 2004 - add 7 (age this year) = 11
Grandson Ryan - born 2010 - add 1 (age this year) = 11
Still cool, though!