Yes but the area training takes so much more time that even if you start when you're 18 you will (normally) be 21 when you're done. If you do aerodrome only you may not even be at the college for 6 months (in theory) whereas area is at least 11 months just at the college. This is even more the case now when the courses have (or so I'm told) been streamlined even more.
Looking at the people at the college I would hazard a guess that being 18 is not a disadvantage in itself (fact is they're not allow to look at age at all since it can be considered discrimination) but most people are over 20 and that is probably since you will in general be more experienced and better prepared for the training with a few more years of life before you start. Not saying you shouldn't apply, but I have heard of people who were turned down at 18 and told to get some more experience, then they came back a few years later and made it in.