If teachers have the right skills and receive support, they could be running secondary schools while still in their 20s, said Steve Munby, chief executive of the National College for School Leadership, Nottingham.
More money should also be given to heads in areas which are struggling to recruit, he said.
"There should be rigorous diagnostics in the first few years of being a teacher, followed by a fast-track system," said Mr Munby.
The number of school leader retirements is likely to rise from 2,250 in 2004 to a peak of nearly 3,500 in 2009, before falling back to around 2,500 in 2016.
According to figures from the General Teaching Council of Wales, more than 1,100 Welsh heads (65 per cent) are aged 50 or more. Both Welsh and English primary schools are receiving fewer applications for headship posts, down from an average 5.4 to 4.8, according to Education Data Services (EDS).
But in Welsh secondary schools, government statistics suggest application numbers average 22 per leadership post - compared with just eight in the EDS survey (TES Cymru, September 8).
The Assembly government insists it has taken into account a predicted increase in headship turnover by 2010 by ensuring enough potential school leaders are undertaking the National Professional Qualification for Headship.
Mr Munby said: "The average age of heads in their first headship is 42. If it continues to take 20 years to become a head, we will not have enough."