I was about 14-15, as it was when I was in year 10.
That was to one of my best friends, who took it pretty well- Then I told another friend form school sometime later, who told a few people but he and thy took it well. Then I told a nother friend who I thought I could trust and the next day the whole school (being 50% homophobic) knew.
Now though I'm at a different school (yay for 6th form!) and everyone there has been great about it.