Have broken a steel fork on our tandem after 13,000 miles.
Currently have a carbon fork/steerer on our tandem with only 34,000+ miles on it.
Single bike has c/f fork with 15,000+ miles on it.
Note: it is not how OLD your bike/fork is; the mileage is a better indicator than the age.
Too man bikes are 'old' but have minimal miles on them.