time posted after fixed moment

I’ve tried looking though this and a bucketload of other forums, and I’ve also tried to find what I want to do in php documentation, but either I’m just being very stupid or I can’t find it anywhere.

I want to make the post times on a blog display as the time since a fixed date. The reason for this is this to display the age of the poster, with the date of birth being the fixed date. So it would display as something like ‘Posted when I was 20 years, 6, months, and 3 days old.’

If anyone has any ideas on how I can do this, I’d be really grateful for any advice/help.

thanks, John