4 year old Default

Depends on the lender, the product applied for, the amount of the default, whether it is settled or not, whether the person has other accounts with a good credit history etc.

So overall it is hard to say.
For mainstream lenders it is likely to have an impact of a person's ability to borrow and the rate they can borrow at.
For some subprime type lenders it may not have as big an impact.

Places willing to lend to (what are perceived to be) higher risk customers, but at expensive rates.

E.g. credit cards there are a number of providers who will offer credit files with low credit limits and APRs of perhaps 40% - 60% (vanquis and aqua are examples)
Or for mortgages there are lenders who will offer a much lower loan to value with higher intital fees and higher APRs (these are usually best found by using an independant mortgage broker).

Most sub prime mortgage lender will ignore a default after three years.