A young kickboxer has spent his first night in jail since he was sentenced to at least six years behind bars over the one-punch death of a retiree.

In sentencing Kaine Geoffrey Jones for manslaughter on Friday, Justice Ian Harrison said the Muay Thai boxer behaved in an "unacceptably angry and aggressive manner".

Jones, 25, fatally struck Graeme Wilton after they got into a loud argument during the retiree's evening walk in December 2013.

The 56-year-old was staying at a Lake Macquarie caravan park with his wife as part of a year-long holiday around Australia.

"Mr Wilton was a vulnerable person with no opportunity to anticipate or prevent what occurred," Justice Harrison said in the NSW Supreme Court.

The judge gave Jones a maximum sentence of 10 years, noting he had no history of prior violent offences, had shown genuine remorse and had good prospects for rehabilitation.

With time already served he will be eligible for parole in July 2021.