How to determine age of HEAD commit

[Philip Oakley <philipoakley@iee.email>]

The Visual Studio git solution uses the vcpkg manager for dependencies, 
via a cloned git repo.

To avoid repeated probing for updates when compiling, I considered 
holding of on 'git pull' for the repo for say 24 hours (daily update). 
However I'm not aware of a git command that returns the numeric value of 
the agedness of a given local commit (typically HEAD).

Is there a command that does return the numeric agedness of a commit 
(e.g. now - commit_date, in seconds)?
--
Philip