I would say it would depend on the storing conditions, Some seeds stored correctly could last years+++.

Many edible fruit seed can not be stored for long periods. They needs to be kept moist as still in the fruit or they lose the ability to germinate. This is true of apples, pears, etc. It is also true of citrus fruit. I'm pretty sure Mangoes are the same way.
Remy

so im guessing this applies to avocados too. thanks you two.

2000 years. The oldest seed to germinate was estimated at 2000 years old.

Maybe - but it wasn't a Mango. They lose viability quickly.

I believe that its the same blue sky and within the shell its a perfect environment and the ability to germinate now or in the future is of course speculation but they are prone to the same conditions of rot, mold, virus or plenty of other plant diseases but the possibility is always there and in mangos for example one never knows until the outer shell is cracked and the inner seed is inspected.

I tried to germinate a dried two week old mango seed, twice. It will not germinate. The ones I wrapped in wet paper towels until sprouted and then planted did grow into trees.