How many years Magento 2 certificate is valid?
--> It is valid for Two years only.
How much time it will take to prepare for Magento 2 exam?
--> Depending upon you, it will take upto 3 months if you are preparing in good way.
If Magento upgraded to magento 3 4...then the certificate is acceptable or not?
--> No, Magento 2 certification is valid only ...