I remember I started offering prayers at a very early age, ever since I don’t have any qaza namaz but still i am not sure whether I started offering prayers at an exact age of 9 or not. So, if not, how can I offer the qaza prayers as I am not sure how many these are?

As you mentioned that you started praying in early age get help from elders in what age you started praying In’Sha’Allah it will help you to calculate one. Remember one more thing 9 years according to lunar calendar Islamic calendar which means you became Baligh 99 days before you completed your 9 years.