It evolves at level 21.
21
Bellsprout evolves into a Weepinbell at level 21 in Pokemon Crystal.
Bellsprout evolves into Weepinbel at level 21.
bellsprout and what they evolve into
evolve from bellsprout
No, you should not raise a Bellsprout at all. Bellsprout is a grass Pokemon, and grass Pokemon (that aren't starter Pokemon) are weak Pokemon. Plus, if you do not evolve him, Bellsprout would be a drag and provides no use other than an HM slave (where you teach a single Pokemon multiple HM moves).
Bellsprout evolves at level 21.
Level 21
Bellsprout evolves into Weepinbell at level 21. Use leaf stone to evolve Weepinbell.
It evolves into a Weepinbell at level 21.
Bellsprout evolves into Weepinbell at level 21.
let him eat rare candy