Green’s Dictionary of Slang

an excl. of satisfaction.

1983		J. Sullivan ‘Wanted’ Only Fools and Horses [TV script] The paint? Yeah, ace!
1999		Guardian G2 22 July 22: Wow! Woo-hoo! Fantastic! Ace! Amazing!
2000		N. Griffiths Grits 24: A drive over a pothole down Cwmparden lane an hear somethin start tuh grind in thuh engine. Nnnnnnnnnnnnnnnnnn. Ace.