Age will be irrelevant.
Coming from an engineering background, especially already a marine one, will help. Emphasise your engineering and technical skills, not exactly sure what you do for a marine technology degree, but anything to do with fish, mamals and the environment – forget it. Concentrate on the electrical, electronic and hydraulic side of your skills, or do courses to build up any side of this that you are weaker on.
There is certainly no reason why you could not get a job as a trainee – we have ex-gun technician got a job with us.
Does the company your working for currently do ROVs, is there any chance of getting a job as a trainee with them? As what Scott said, have a read through the site, have a look at Rons ROV Links site. Have a read through the FAQs on the site here as well.