Chrissy,
There are many 18 year olds at or have recently been through the college, many with a great further distance to travel than from Wales.
Don't let your age be a factor in applying for what I believe is the best ATC career option this country has to offer.
Many people leave home at a young age to pursue their careers, I left home when I was 17 to join the RAF, and didn't look back (until 7 years down the line when I realised the RAF was in fact not the best career move I could have made.)
In conclusion if you want to be an ATCO, apply for NATS, live away from home, do the hard work, have the ups and downs that training brings, then when its all behind you, you can enjoy the good life that you have worked so hard for.