Aga captained Kenya in the Intercontinental Cup final in November 2004 after making his international debut in the 2003/04 season.
He was also skipper of the Kenya Under-19 side, but has had little time to pursue his international claims since, spending much of his time studying in Britain.
He has a British passport and was snapped up by Sussex in 2007, playing in one NatWest Pro40 match in which he took one wicket.
He was given a further county contract for the 2008 season, where he made five first-class appearances and finished as the leading wicket-taker for Sussex's second-string.
Aga signed a further two-year deal at the end of the year.