enlistment age

[jabwok]

My grandfather, John Watson #9810, pay book (from WWI) shows his attestation date as Feb 24, 1906. He was subsequently moved to reserve status and was called up in 1914.

The family thinks he lied about his age when he signed up. I would like to know what the enlistment age was in 1906, and what the term of service would before being moved to reserve status.

Thank you,

Judith