his age shouldn't be a problem. He's still young enough to bounce back quickly. Just make sure you have pre-op bloodwork done before surgery to make sure he can handle the anesthesia (this should be done before any surgery no matter the age).
As for staying over night, personally i do not think its necessary for something as simple as a neuter. If there is staff at the hosp 24/7 and they insist he needs to stay then fine. however if no one is there over night, i would not leave him. he's better off at home where he can be monitored instead of in an empty hospital in a cage. Neuters on healthy dogs are just so simple and quick that its usually not necessary for them to stay in hospital for more then a few hours if they recover well.
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