Is this agenda card only available in Joust (or as I understand..when only 2 people are playing)??

The card has been erratad to "Joust format only", which means it can't be used in Melee (3+ players) or, technically, any of the alternate formats (hand of the king, civil war, kingsmoot) - although the latter point is mostly irrelevant.

So, as you say, only available in the head-to-head (2 player) matches.

This was mostly because if you had 2 or more Old Ways, their effects added up and completely changed the melee game; defending a challenge and counting less strength could cost you 2-4 defenders!

thanks!