At the
2009 World Youth Championships in Athletics in
Brixen, Italy, Koech won a
gold medal over 3000 metres, setting a new world youth leading time with 7:51.51. He also took part in the
2010 IAAF World Cross Country Championships in
Bydgoszcz, Poland, finishing fourth in the junior men's race. On 11 February 2011, Koech became just the fourth man to run the 5000 m indoor under 13 minutes when he clinched victory in 12 min 53.29 sec at the
PSD Bank Meeting in
Düsseldorf. He then ran a world junior indoor best for the 3000 m at the
Indoor Flanders Meeting a few days later, running a time of 7:37.50 minutes Koech controlled the junior race at the
Kenyan Cross Country Championships and took first place, earning a spot for the Junior World Cross. Despite being a provisional favourite for the junior race at the
2011 IAAF World Cross Country Championships, he ended the race in tenth place. However, he did help Kenya to the team title alongside
Geoffrey Kipsang and
Patrick Mutunga Mwikya. Moving into the senior ranks, he ran over 5000 m at the
2011 World Championships in Athletics and closely finished behind the medallists to place fourth overall. In December, he returned to cross country and won the
Lotto Cross Cup Brussels by a margin of over half a minute. At the 2012 Kenyan Olympic trials he ran the fastest ever 5000 m time in Kenya to win the race and guarantee his first Olympic selection. ==Personal bests==