A teachers' union has claimed there could be a shortage of head teachers in Wales because of the ageing workforce and recruitment difficulties.
The assembly government says Wales has enough head teachers
Figures show two-thirds of heads could retire in the next decade.
The National Association of Head Teachers also warned extra workloads and long hours put new recruits off.
The General Teaching Council said it was training a new generation, and the assembly government said Wales was well served in the pool of future heads.
Figures from the General Teaching Council of Wales (GTCW), the body which regulates teachers in Wales, show that just over 66% of heads wereaged 50 or over.
GTCW chief executive Gary Brace said most head teachers would naturally fall into the older age bracket because of the experience and expertise needed for the role.
But the National Association of Head Teachers (NAHT) said the statistics revealed "potentially a very serious problem" for schools.
It also claimed that schools were finding it increasingly difficult to recruit heads willing to take on an increasingly demanding role.
"Many of our members are running two schools at the moment," said Iwan Guy from NAHT Cymru.
"The pressure they are under is immense.
"Head teachers get blamed for everything - poor inspections, bad behaviour. No wonder there are record numbers of head teachers away with stress.
"I know colleagues who would say, 'if I could quit I would'."
John Bibby, headteacher at Goetre Junior School in Merthyr Tydfil, said the job did have "a big workload" but that he found the position rewarding.
"I enjoy my job but I also think there is a general ignorance as to what teaching in general entails and what headship entails - it is an extremely demanding role," he said.
To become a head teacher in the UK, applicants are required to pass the National Professional Qualification for Headship (NPQH) qualification.
But Mr Guy said many of those who had passed the qualification in Wales had no interest in going on to apply for headships.
"It's not the money, it's because of the job itself," he said.
Heledd Hayes from the National Union of Teachers (NUT) Cymru said the effect on schools of not having a full time head could be destabilising for staff.
However, Mr Brace of GTCW said its statistics showed there was an increase in the number of NPQH-qualified teachers rising through the ranks who could take the place of those retiring over the next 10 years.
He said 250 out of the 1000 teachers who had achieved the headship qualification had gained a headship.
A total of 170 were currently going through the NPQH with another 149 accepted on the course in the latest recruitment round, he added.
A recent Estyn survey also found for every head teacher post advertised there were between 6 and 15 applicants.
Mr Brace also highlighted that the number of teachers in their early 40's who hold the NPQH had increased over the last five years from 9% to 12% of the total.
But he said the GTCW would endeavour to make school leadership "a far more attractive proposition and encourage those with the NPQH to go for it".