Almost half of permanent teachers, heads of department, principals and their deputies, or around 11 600 people, were 50 or older, The Cape Times reported.
The department employed 31 628 teachers, of whom 2 942 were on contract.
The figures were revealed by provincial education department human resources director Ivan Carolus in the provincial legislature on Tuesday.
Education standing committee chairperson Cathy Labuschagne said the figures were concerning.
Carolus said the department was closely monitoring the situation.
"We believe we have a sufficient number of graduates to address the teachers who retire or fill vacancies," he said.
He said the department would advertise four vacancy lists this year to appoint teachers where schools needed them.
Education MEC Donald Grant reportedly said around 800 students graduated each year and that the department could not place most of them.