In respect to this, is STA Travel legit?
They are 100% legit and I highly recommend them! I have used STA for two trips to Europe. Just for the airline because they have the cheapest flights I can find. But that card is a scam don't get it.
Furthermore, can you use STA travel if you are not a student? You do not need to be a student.
Keeping this in consideration, is my flight Atol protected?
If you booked a flight-only deal through a travel agent, you may be covered by the ATOL (Air Travel Organiser's Licence) scheme. BUT not all flight-only deals are. You will be covered if: the agent is ATOL-protected; or you received an official ATOL receipt upon payment.
Does Atol protection cover flight cancellation?
Bear in mind though that while ATOL protection may mean you get a refund for your flight and/or package holiday, it won't cover other elements booked separately that you can't use if your holiday is off – for example, if you've booked separate hotels or car hire.