There are old wallets like wallets from 2012 that might look old and forgotten, it can be very difficult to recover funds inside and for a person that thinks all hope is lost due to how complex it is to recover that kind of walle. The owner will be very happy if their funds can be removed from the wallet. I know some examples of old Bitcoin wallet like multibit that lost continuation in development stage due hugs and the team discontinuing and developing the wallet. That kind of wallet can be very difficult to recover funds in it even when you use sophisticated tools.
The issue is not how long the wallet has been lost. Where the issues lie is what amount of information the owner can provide in other to restore the wallet. With the right information, any wallet can be recovered easily for the wallet recovery services whether old or recent wallet, but when the information is not too clear it becomes a problem and it will take longer for them to recover the wallet. And yeah, the expenses will increase because the recovery service will demand more money to do that.