Add and Display Custom Field Last modified date on Customer Record

1.  Navigate to Customization > Lists, Records, & Fields > Entity Fields > New. 
2.  Enter a Label (i.e. Last Modified). 
3.  Type = Date. 
4.  Uncheck Store Value. 
5.  In the Applies To tab, place a check mark on Customer. 
6.  Click the Display tab > Subtab field, select Main. 
7.  In the Validation & Defaulting tab, enter {lastmodifieddate} in the Default Value field and place a check mark on Formula box. 
8.  Click Save.