Probably his insurer just doesnt want that type of business.
My mum is in her late 40s and has an RX8 (admittedly only the 190 one) and pays £300 or so per year fully comp with my dad also as a named driver.
She has 9 years no claims or something silly, the maximum they'd let her enter on the webpage form, and an SP30 about 3 years ago.
This is with Norwich Union (iirc)
On the other hand CIS (co-operative insurance) who were her previous insurers and she had been with them claim free for 6 years, refused to even quote for it unless she had a tracker fitted. Having seen the Norwich Union quote, it wasnt even worth looking into the price of a tracker.
So, in conclusion, it could just be the insurers way of saying "sorry, we dont go for customers with cars like that" - get him to do a quote elsewhere.