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