I am 16, and will not be 17 until June... Although I do generally hang out with people older than me (most of my friends are 18/19), and so often catch myself patronising 17-year-olds...
Like you, Jenni, I am rarely asked for ID, mainly because nobody really cares... I have been asked for ID once, when the barmaid said that the manager was coming out to check everyone's... All that meant was that one of my friends had to buy the drink for me...
Actually, I think it's partly luck. I have this knack to not be noticed when it suits me... Case Study 1: The Gallery (a nightclub near me). You aren't allowed in until you're 18, you must be smartky dressed, and you must be sober. I was 15, dressed in a t-shirt, jeans, and trainers, and I was totally wankered, and I wandered in without paying, while the bouncer was busy with my friend Dave (19, but always likes to take ages finding his ID whenever he is asked for it, just to piss off whoever is asking...

)...
Got a bit off-topic there, sorry... Ah well, variety is the spice of life...