I am aware all boats are manufactured to different specs. But with the common mclay, fyran, ramco etc are the hulls still likely to have a lot of life left at 25 years of age?

I had a 2017 alloy pontoon boat that at 4years old had a hole corroded through the hull stepdad brought an alloy boat of another brand that at 20 years old that he soon found out had many pinholes corroded through the hull.

Theres also many 20-30 year old hulls that are going strong, just depends on the construvtion, design and maintenance. Best to carefully inspect any boat your interested in rather than some someone telling you for example that all 25 year old ramcos are good.