Custom date formatting (days old)

Hi all,

Not sure if this is a plug-in or likely to be PHP code.
I am looking to replace my post time stamps/date formatting with something like the below examples:

This would be for a post that is 1 day old:

Age: 1d

This would be for a post that is 2 day, 1 month old:

Age: 1m 2d

This would be for a post that is 2 year 2 day, 1 month old:

Age: 2y 1m 2d

Hope all this makes sense, and I have explained it all clearly, but it would be great if someone could shed some light on this, and get me one step closer to getting my blog finished 🙂

Thanks all