Everyone's definition will vary slightly. In my opinion there are two components to being a BL:

1. Romantically or emotionally attracted to young boys (capable of falling in love with a boy).
2. Sexually attracted to young boys.

The definition of boy will vary on a per person basis as well. But in my opinion, to classify as a BL and not just a gay person who is into younger guuys, the boys you are attracted to should be pre-pubescent or barely pubescent.

A BL is, by definition, a pedophile. By virtue of being sexually attracted to young boys, you are automatically a pedophile.

However, a pedophile is not necessarily a BL. Some pedophiles view boys as sexual objects and thus do not fit criteria #1.