Green’s Dictionary of Slang

aces adj.

[ace n. (3)]

1. [20C+] (US) of both people and objects, wonderful, marvellous, excellent; thus you’re aces!

2. [20C+] (US, also aces up) esteemed, well-respected, favoured.

In phrases

aces and eights (adj.) [poss. misreading of the usual idea of bad luck in a hand of aces and eights (that supposedly held by Wild Bill Hickok when he was gunned down on 2 August 1876)]

[20C] wonderful, marvellous, excellent.

aces up (adj.)

[1900s] (US) on very good terms.