Possibly another stick, if it would be useful. (All the below predicated on you being in England or Wales, and the seller having owned the property for more than 3 years).
the first report says the wiring is 3 years old
So - the seller commissioned and gave you, as part of the sale, a document which said the wiring was 3 years old.
Were that to be true, it would have required notification to Building Control and should have a completion certificate showing that it complied with the Building Regulations.
What did the seller say on the questionnaire about notifiable work, and Building Regulations certification?
If he said none had been done, then there you have cast iron proof that he knew the report was false.
If he said that the house had been rewired in 2017, where's the documentation? Did he notify it? If not, that's a criminal offence.
In your shoes I'd be seeking to destabilise him - to go after him on as many fronts as possible, make the penny drop that whatever story he tries it's going to poke holes in an another one.
If it looks like he knowingly lied, press the police to investigate an offence under Section 2 of the Fraud Act 2006 - Fraud by false representation. We all know that he isn't going to end up being charged, but just one visit from the boys in blue won't half put the wind up him.