I really wouldn't worry about age, I would worry about condition.
If the aeroplane is dirty, the seats are ripped, there are visible loose wires from the instrument panel, then you've got good grounds to question how well the engineering is looked after also.
If it's clean, complete, the visible maintenance is tidy, the paperwork's up to date, and it's 50 years old, the odds are it's as safe as if it had just left the factory.
G