If you mean for Cadet entry, you're in the wrong thread - there's a separate one for the Wings Cadet scheme. The answer to your question, however, can be found on the CTC Wings Cadets "Qualifications" page:
http://www.ctcaviation.com/wings/040201.html
which states...
"On the date of application you must be at least 18 years old and not yet 30 years old."
Similarly, for the Wings ATP scheme, on the relevant page:
"On the date of application you must be aged between 19 years and 34 years (within 3 months of your 34th birthday)".