Rank of Customer

I'm trying to use the Rank feature.  I want to rank the Top Record of Each Customer.  I have a customer that can be listed multiple times in this dataset.  I only want the record with the oldest date.  I used the ranking, but it ranks the entire dataset, 1-8400, instead of giving me:

Cust ID   rank   

123            1

123            2

234            1

234            2