which essentially means that all
@burberri333 can do at this stage is wait and see if they get contacted within the next 6 to 8 months, by keeping an eye on their post, e-mail and spam.
When they receive something they should return here to ask for specific advice on how to respond to that.
The OP needs to consider (and they don't need to say it here) if there are other times they have bought child fares after they turned 16 years of age, as it is likely the railway company will ask them about that and will have checked on line ticket buying to see if there is evidence of this happening.
meanwhile the OP should buy a 16-17 Saver Railcard so they can buy fares at a discount (which means the ticket is the same rate as child fares) and use them to travel without breaking the law. In my view they should do this as soon as possible as it will show the op has 'learned a lesson' which is the sort of thing the Railway want to see when investigating things.
see:
50% off Rail Fares for just £35 with the 16-17 Saver Railcard. Enjoy great train journeys for less - Buy Now.
www.16-17saver.co.uk