Saddle for the Mature B-Boy

Sorry this is wrong.

Specialized saddles come in different widths; on their MTB team a few years back the guy who was build like a wippet and had no kind of arse or hips had the widest seat bones and therefore used the widest saddle...

I think when people say arse, they mean sit bones TBH.

^ this.

Have you used the specialized arse measuring tool?

It helps you locate you sit bones and measure the distance, so you can take that figure and apply it to your purchase of a specialized saddle.

You can also use this figure to help identify which other saddles may be appropriate.

I didn't mean it was just a massive set of callipers to assess the size of your junk a la

I think you need to consider the following:

Sit bone width (specialized have a scale for this)
Flexibility, or riding position (Fizik have a scale for this)
Weight (Selle San Marco have a scale for this)

...and even then it would still be trial and error.

Also good advice.

I still think a £30 second hand B17 is a worthwhile investment. If he doesn't like it he can resell at cost.