British Cycling classifieds might be a good place to look - there are often parents selling the bikes that their kids have outgrown (really sorry if that comes across as patronising, but I'm sure you're aware that there are plenty of teenage boys taller than you!). And I mean 'proper' bikes, not crappy mountain bikes like my childhood bikes were. Usually road/cyclocross.
British Cycling classifieds might be a good place to look - there are often parents selling the bikes that their kids have outgrown (really sorry if that comes across as patronising, but I'm sure you're aware that there are plenty of teenage boys taller than you!). And I mean 'proper' bikes, not crappy mountain bikes like my childhood bikes were. Usually road/cyclocross.