The minimum age for this licence is 18 years old and you must hold a full Cat C and Provisional Cat C+E licence. You MUST pass Cat C first.
Having passed the Cat C test you can now undertake the practical driver training for the C+E. Train to the DSA test standard and take the test. There is no set time that you are required to hold the full Cat C before progressing to C+E.
On passing the test: You are licensed to drive any lorry towing a trailer.