Averaging Variable Number of Cells

I'm looking to do a rolling average where the user enters x number of years and it averages over those x years over time. The data set looks as follows:

Column A has dates from a to b in descending order (date b is first and date is a is last)
Column B has data that corresponds to each date
Column C should have a rolling average over time. For example if x is set to 1 the first entry should be the average of data points 1 to 365, the second entry should be the average of data points 2 to 366, etc. The problem is, I am unsure of how to get the range that is averaged to changed based on what x is set to. For example if x is set to 2, then it should be averaging data points 1 to 730.

Any formula to help me achieve this would be great. Don't need the formula to be contained within a single column, I am open to using multiple columns to achieve this result.

Many thanks!

I have attached an example. Column C755 has the first entry since I am taking a 3-year average as an example. I am looking to be able to change cell H1 which would dynamically change the number of years being averaged.

Thank you all!

Thanks. Don't see any attached file, but will definitely take a look once posted. Also, I'm looking to avoid Pivot Tables. I was hoping to do it using formula(s) only.

Thank you so much! That formula is exactly what I need! Why copied from the bottom up? I can't just drag it down from the top?