Complex sentence: The minimum age to drive a HGV1 vehicle was reduced to 18 however certain vehicles e.g. steam rollers require you to be of 21 years of age before you are allowed to obtain a license for this type.
Split into simpler sentences: The minimum age to drive a HGV1 vehicle was reduced to 18. However, certain vehicles, e.g. steam rollers, require you to be of 21 years of age before being allowed to obtain a license for this type.