It's been discussed endlessly.
There is no specific age. It boils down to it being a worthwhile and significant design or individual boat.
There is plenty of old rubbish and some newer classics. An visa versa.
Hi there
I have a 1974 Shipman 28, and when I enroll to the classic regata in hong Kong last week they told me that it is NOT a classic but an "antique"....
I did buy that Allegro!!!! It was a toss up between a Lancia Fulvia and Allegro. What a mistake.
The first thing to go was the gearbox, so I removed engine and box separated them and stripped the box. After pricing up the parts it was much cheaper to part exchange for a recon, so I rebuilt the gearbox and got a recon
Next the engine went so out comes the unit........... I can't go on as I'm getting too depressed.