hey,
I started when I was 16 when I was still at school and my parents got me a trial lesson for my birthday. I now have my PPL and currently studying the ATPL theory - now 20.
maths and physics will help out a great deal if your studying them currently at school?
I live in scotland but if I am correct denham may be your closest airfield? pay a visit to them and speak to some of the instructors about flying lessons. cost is a big consideration to your training, don't be overwhelmed at shiney new glass cockpit aircraft costing £140 ish per hour, a C152 or PA-28 140 at about £80 is adequate for initial training. ask instructors about their experience and dont dive right in, visit other local airfields and consider them too.
all the best!