I don't consider giving up an instrument, or an avocation like fishing (especially since it provides us with food at little expense, LOL)...to be limiting one's possibilities. Our son is a bit of an overachiever, (he's 21 and about to earn his Master's) so I do think it's "healthy" when he takes time off to enjoy things other than studying (he's been in college classes since he was 16.) Different strokes for different folks.
During my years of studying, I played piano, had friends, went out, drank to excess at times, partied. But it was not alot, was infrequent and never interfered with the studying.
Your child is getting amessage from you that it is “unhealthy” to buckle down and give up fishing as much. He is hearing you say “he needs a break”.
There is no break in life,,he is way young to “need a break”. Kids who take a break see themselves as weak or fragile. He is 21 and has done well,,I don’t believe in the whole “overachiever” thing,,it implies he did better than he should have.
LIfe is long,,to start “needing breaks” at 21 is not a good idea in my mind,,