Maple Syrup as long as it remains sealed will last for 10 years or more but most people use the maple syrup up sooner than that.
I've kept unopened maple syrup before for 10 years when I bought a case of it on sale and stored it in the pantry and the maple syrup was perfectly fine after it was 10 years old.
But once you open the bottle of maple syrup it will last around 3 to 6 months before it starts to go bad.
However maple syrup will lose it's freshness after a year even unopened and when opened the maple syrup will lose it's freshness after the year.
If you freeze the maple syrup it makes the maple syrup last a very long time and basically forever.