Nathan, you wouldn't hold a full ATPL until something like 1500 hours flying time down the line. Even if applying at 18, it'll take you more than 3 years to achieve that when you take into account the duration of the application process (roughly 5 months), the wait to commence training (likely anything from 6 to 15 months, going by this year's stats), the training itself (say 16 to 18 months, including type rating) then working full time on the line with a maximum of 900 hours per year. No way you'd reach that point before age 21, so nothing to worry about.
Edit: beaten to it by G-FORC3
