My Staryu is level 58 right now. Should I go ahead and evolve it or wait till a different level?
No, LV it up to LV 60 so you can at least learn Hydro Pump. If you do not want to get Hydro Pump, then it is fine to evolve it now because it will no longer learn other moves than Hydro Pump at LV 60. Hope this helps...
Staryu learns Hydro Pump and level 60 in Black/White so if you're playing those games, and want that move, then wait two more levels.
Otherwise you might as well go ahead and evolve it!
Staryu learns Hydro Pump and level 60 in Black/White if you evolve it young staryu will not easily learn a Hydro Pump