Man, can you imagine having to decide how you were going to look for the rest of your life (hair style, tattoos, piercings, musculature, body mass...) at age 20? It'd be like when you picked your AIM screen name at age 10 and then had to tell it to people in college.

[Minor nit: genes are insufficient to record someone's physical state.]

[Minor nit: I'd argue age 25-30 is probably a better physical peak to snapshot than age 20.]