This is a shortening of the word “legend.” A legend is someone who is well-known, often for doing something great or incredible. The slang word “ledge” is often an exaggeration, or used to make things and people sound more important than they really are. It can be used not only to describe a famous person, but also a friend or family member who is not famous. It is often used when the friend or family member has done something particularly good or impressive.

“That final goal was amazing, mate. You’re a ledge!”

“Thanks for the tickets, mum. What a ledge!”