Green’s Dictionary of Slang

about that adj.

(US campus) in agreement with.

Online Sl. Dict. [Internet] about that adj. 1. in support of. Also about it. Note: often pronounced ‘bout that’ or ‘bout it’. (‘I’m so not about that.’ ‘You want to leave now? I’m about it.’ ‘Whatever you want to do, I’m about it.’).
[US]Eble Campus Sl. Apr.

In phrases

about that life

(US campus) in agreement with.

[US]Eble UNC-CH Campus Sl. Spring 2014 1: ABOUT THAT LIFE -- in accord with a particular way of living: ‘I just dropped a couple hundred on the new J’s [Michael Jordan sneakers] . You know, I’m about that life.’.