As Hc4361 has indicated, the law (as applied to a young person) only relates to the purchase or possession of alcohol, not to actually drinking it. A person under 18 commits an offence if they try to buy alcohol, and police are empowered to seize alcohol from minors in a public place, but it's not an offence for a young person to consume alcohol.
As far as the young person (and the law) is concerned, they're free to drink alcohol from the age where they can hold the glass or bottle (which might be around 1 year old!). However others can commit an offence by supplying the alcohol (or by permitting them to consume it on licensed premises).
Your username, RyanBoyd97, suggests that you're probably 14 or 15 years old. If you can get hold of alcohol it's perfectly legal for you to consume it (but if you do so in a public place you risk having it seized by the police).
However it would be irresponsible of me not to point out that many young people exceed the accepted safe limits for consuming alcohol:
http://www.patient.co...Limits-of-Alcohol.htm
(Even going marginally over those limits can considerably increase certain health risks).
Equally, I'd be hypocritical if I failed to mention that my first serious drinking session with my pals was on my 14th birthday (at home, with the full consent of my parents) and that I'm currently somewhat further down a bottle of red wine wine than the recommended guidelines allow!
Chris