haiste

Hi, I have been approached by my employer in the UK with a view of emigrating to Australia and starting a new job down under. When it comes to the visa what I am being offered is:- They will bring me and my family in on one 457 visa, this is valid for 4 years and at 2 years in they sponsor me through to permanent residency (subclass 186), again this includes all family and dependents. My question is my oldest son is 18 years old in September and would like to look for an apprenticeship in engineering. would his age be a problem with the visa that I am being offered and what would be the attitude of prospective employers towards employing a newly arrived 18 year old? would he have an equal chance of finding an apprenticeship. would he be classed as a dependent when he is 20 years old and an apprentice?