If the debt was statute barred (ie no payment made and no acknowledgement of the debt made for 6 years) when he was approached in 2003, then it is still statute barred. If it was not statute barred at that time, then the payments have prevented it becoming statute barred, & it will only become so if no payment is made, & no acknowledgement made, for the next 6 years.
All this assumes the creditor did not get a County Court Judgement for the debt before it ever became statute barred - if they did, then in theory it can be enforced for ever.
If the debt does relate to an account closed over 20 years ago then the likelihood is that it is statute barred. Insist on getting full details and don't pay anything more until they are provided.