Osano competed for Kenya at an early age and as a junior athlete he shared in a team silver at the 1987 IAAF World Cross Country Championships (led by winner Wilfred Kirochi) before returning in 1989 to finish fourth and help Kenya to the team title alongside individual medallists Kipyego Kororia and Stephenson Nyamau. He won an individual medal at the 1988 World Junior Championships in Athletics, entering the 20K run, where he was runner-up to Ethiopia's Zeleke Metaferia.