This originates from the AXA superanuation slogan "AXA, Investment for the future".
The whole idea of an AXA is to try and become freinds with them early so that you can bang then when they are at a reasonable age.
Guy 2: Man that's just wrong, she is 13 and your 17.
Guy 1: Yeah I know, I just mean that she is an AXA.
Guy 2: I feel that. Her mum is hot too. So she'll probably look like her when she is older.
Guy 1: Yeh, true... Definatley an AXA.
Guy 1 and 2 - Calling out: "JESS, DO YOU WANT TO COME AND WATCH TV WITH US?"
A person who is young, but would obviously be attractive when they were older.. used to avoid looking like a cradle snatcher.