He began training alongside Edwin Soi and made his breakthrough in the 2009 season. After finishing second to Peter Lagat in the 2000 metres steeplechase at the national youth trials he was chosen for the 2009 World Youth Championships in Athletics. There he beat his Kenyan rival in the final stretch of the race, winning the gold medal in a time of 5:25.33 minutes in spite of his poor hurdling technique. Yego attempted to gain qualification for the senior event at the Kenyan World trials 3000 metres steeplechase race, but finished in ninth place. A third-place finish at the national junior trials the following year meant he missed a berth for the steeplechase at the 2010 World Junior Championships in Athletics. He ran on the European circuit for the first time that year and set a best of 8:19.50 minutes for third at the KBC Night of Athletics.