I agree with Carole - back in the day no evidence of the age of the deceased was required - only the word of the person registering the death.
I had a similar experience with a death registered, showing the deceased to be 10 years younger than they actually were. I ordered the death certificate and it was definitely my ancestor, as it had been registered by her son in law.
If you are unsure, order a PDF copy of the death certificate from the GRO - unless they have died in a hospital or the like, you can hopefully tell whether it's the correct person by the address, occupation and informant.