Calculating Previous Sales Date

I have an interesting issue I need help figuring out.

I have a table that is a list of orders (columns like order date, name, product, price, etc). 

I have been requested to create a measure that displays the number of new or returning customers from this data (new/returning being a customer who made a purchase that had not made a purchase in the last 3 years).

My thoughts for doing this would be to take the table I have and add a column that shows the previous date that customer made a purchase, if it was in the last 3 years. So for example, if customer A has an order date of 12/15/2023 and 5/27/2022, the order date of this table would be 12/15/2023, as it already is. There would be a new column (called last order date) that displays 5/27/2022. If the customer in the order data does not have a previous order date in the last 3 years, then the column will just display a null. 

To continue the example, lets say customer B has an order date of 1/1/2023, and 1/1/2009. In this example order date would display 1/1/2023, and last order date would just display "null" (it was longer than 3 years ago). 

With this I could just take a distinct count of customer numbers where the last order date is null, since that signifies they either have never ordered before, or it was more than 3 years ago. 

Can someone guide me through how to create this custom column that will display the previous date a customer ordered, and null if its longer than 3 years from the current day?

Thanks!