The UN came to be when the UN Charter was signed in San Fransico in June of '45 (ratified in Oct '45). That made it 61 this year.
I do believe it's been 50 years since Pearson was the catalyst behind the creation of the first United Nations Emergency Force, however. I would assume that's the 50th the PPC is celebrating.
Edited to add: I'd love to go and meet some folks, but I'll be out of NS (done HLTA) and back in the Sandbox by then.