What makes a great PM

I was reading P N Balji's comment on the barriers of age, gender and race. And he mentioned that LKY was a PM at 35, Chok Tong at 49 and Hsien Loong at 52. For this, he suggested that the future PM could be older, maybe in the 60s. This is natural as our population, including the supertalents will live to 100. And if they are not fruitfully employed after 60s, then they will be rotting somewhere