I was reading that Monaco's House of Grimaldi has existed since the 1200's, are there any other monarchies that have stayed in existence for longer? I don't care if they're no longer politically significant (like the British monarchy), just that they are still recognized by the populace.
Do you mean monarchical house or simply the institution of a national monarchy?
This question is also complicated by the fact that institutions will try to claim a direct inheritance from previous institutions where the actual connection might be dubious (for example William I of England claimed to be the heir of the Saxon Edward the Confessor and through him the English line of Alfred of Wessex founded in 880). Other monarchies have mythical origins the further back you go (the British crown can also claim inheritance, via the Crown of Scotland, to Kenneth McAlpin in the 800s... whose existence both as King of the Scots and in itself is disputed).
All that said the Imperial House of Japan is the oldest monarchy being founded in 660 BC... if you believe the legend. Emperor Keitai (500s AD) is the first actually verifiable emperor I think.