Ref the "guys doing the turnarounds".....as has been mentioned these may be carried out by licensed engineers or pilots.
However, a licensed engineer will get involved if there are incoming defects on an aircraft which cannot be deferred. Decisions have to made regarding the airworthiness of an aircraft and rectification often takes place in a pressurised environment (particularly now with the delayed flight compensation culture!
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This is not a career you can amble into. It takes, a lot of training, studying & exams just to get the basic license and plenty more of the same (plus heaps of experience) to become trusted by a company to hold an approval.
It’s possible you could obtain a position as an unlicensed Mech in a hangar environment after your HNC (which is always good place to learn the basic trade) However, the money won't be great and it will depend on your location and ability to travel. If that’s what you choose to do, you'll be able to gain the all-important experience and decide if the career is for you.