its difficult as some cars of similar ages are most definitely not, take early 70's, Capri, Escort etc . . .classic cars in every sense . . . Allegros and Marinas on the other hand, just aren't ( although there are some Quantity surveyors out there who consider them desirable
)
generally 25 years old is getting on for classic status I think
as for old timer . . .is that referring to the cars or the owners/drivers ?