It depends on whether the bike is old or the repairman is old.

We often hyphenate modifying compund words to clarify the meaning:
   My grandfather is an old-furniture salesman.

Sometimes no clarification is needed:
   An antique dealer could also be called an old furniture salesman.

Modifying words preceding the noun are often hyphenated:
   My six-year-old son likes to play with toy cars.
   American-football players are usually men.

Modifying words following the noun are not hyphenated:
   My son is six years old.
   Some men are players of American football.

There are some exceptions, so check a dictionary:
   Time-sensitive documents are those which are time-sensitive.
   A left-handed catcher would catch the baseball left-handed.