G'day,
the reference for this older Richeville is 25200 and in fact it´s a more recent model.
It´s not in production for quite some time and my best guess would be an age of about 10 years.
The dealer who sold the watch should know the delivery date to him, therefore you may get in touch with him?
As an alternative, i´d suggest to get in touch with the GP factory (there´s a contact form on the GP website).
Cheers,
Peter