I purchased and 2021 SuperCrew and was wondering how to tell how old the battery is. It tested fine but do not see a date on it anywhere.

 

Most of the time with a new battery there is a sticker posted on the battery it self maybe on the front or sides. The age of a battery can be determined by looking for a date code. The date code can be found on the top or side of the battery casing. It can also be found on the battery cover or on the battery itself.
The date code may be:
A small label with a letter and a number A strip, engraving, or heat stamp with an alphanumeric code
A 12-digit code with the last 4 digits representing the month and year
A date code that starts with a digit and a letter The first two characters of the date code may contain the date information.
For example, 21 would indicate 2021. The next number would indicate the month. A would be January, B would be February, and so on. The last two numbers may indicate the day of the month.

 

If it's a Motorcraft battery most likely original.

 

The Motorcraft battery in my new-to-me 2013 XLT has a 2018 sticker, and is still going great.