Mr Key's speech continued the theme of the village being tailored to over-50s, predicting that living to 100 would become the norm rather than the exception in years to come.
He said one million New Zealanders would be aged 65 and older within 40 years. And it wasn't all because the baby boomer bulge was moving through the population.
Mr Key said people were living healthier lives and if longevity trends continued where two and a half years were being added to lifespans every 10 years, then the current average age of 80 for men and 82 for women would increase to 100.
"Your kids and grandchildren will live to 100," he told the big gathering in the marquee before he unveiled the plaque.
Mr Key said the interesting thing about Tauranga was that it had moved from having a big older population to being dominated by young families.
However it was still a popular retirement destination, with people coming from Auckland because it was more affordable.
Earlier in the day, Mr Key was given a guided tour of the newly opened Tui Products head office, factory and bulk store at Te Maunga.
He told the 55 staff that the Government was "pretty pro-business" because if people had jobs they could look after themselves and their families.
"It is not really a complex strategy."
The advantage National had was that it was on its own on the centre-right of New Zealand politics, he said. "What you see is that you get."
He stressed the importance of getting more people to vote, saying about one million people did not vote in the last election. "Complacency is a massive risk to us."
Asked later about online voting, Mr Key said that although he intuitively thought it would help, overseas evidence showed voting increased in the first election before slipping back to normal. It would be trialled first by local government elections in New Zealand.
Mayor Stuart Crosby said he understood a trial was being proposed for the Porirua City election in 2016. He supported adding online voting to postal voting, saying it would be particularly useful for younger people who "lived in the online".