jayenm: to quote from GID 21: "Requirements for the issue of a PPL" -
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Student pilots may act as Pilot-in-Command from their 16th birthday provided they act only in accordance with instructions given by a Flying Instructor, hold a valid JAR-FCL Medical Certificate and, generally, fly only in UK territorial airspace. There is no minimum age for dual instruction, but any received before the age of 14 is not countable towards the experience requirements specified in [that] document.
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Hope that helps
-tacc