Student or Learner
They are the same height. They are the same age. We studied that after the same we use a singular noun.
Bob likes the same sports as John. Here when we have *the same...as* can a plural noun be used?
Yes. The rule you learnt applies only when several people each have one of something: 'Their ages are the same' but 'They are all the same age [as John]'.
When they each have several of something, use the plural. Your Bob/John example is fine.