You are very general in your ID of which type of goods vehicle you are referring to. 'Trucks' means many things to many people.
Firstly there are very few employers who pay for driver training from source. Many will build upon what you have to offer but there are many drivers who are already qualified to start with.
If you mean Large Goods Vehicles i.e. those exceeding 7.5 tonnes, you need to be 21 years old anyway.
If you mean Medium sized goods vehicles at your age you will not have cat C1 on your licence and therefore need to be 21 yrs of age and take a second test.
What you can drive on an ordinary licence are light goods vehicles (white vanman) and then maybe hope that the Company involved like your attitude and effort and are prepared to further your driving career with financial assistance.
An alternative, but still needing to be 21 yrs of age, is to join a bus Company and accept their in-house training for a PCV licence. They will then offer a job to successful candidates and absorb the fees for training as long as you stay with them for a predetermined time e.g. two full years.
My advice is to get a driving job on Light goods vehicles and excel at that first. Future training could follow.