Showing latest date before specific date

Thank you for sample data. Here is the code:

Customers with last ticket older than 2 weeks ago = 
var customer_last_ticket =
    MAXX(
        DISTINCT('Sample'[client_id]);
        MAX('Sample'[created_at])
    )
return IF(DATEDIFF(customer_last_ticket;TODAY();DAY)>=14;customer_last_ticket)

In the variable customer_last_ticket we are storing an information about last ticket per customer

Then if this ticket is older than 14 days ago we are displaying int 🙂

I hope that this is what you've wanted.