At what age can a man get a vasectomy?

No legal age limit. There has been no legal age limitation although traditional thought to have children before vasectomy continues exerting its influence to many people's mind. That is understandable, but carries no legal weight to preclude vasectomy. So, it can be done for teens if ... Or for the elderly to prevent epididymitis...
There are. No specific age requirements; it's more the medical or social indications -- but generally not recommended in young males who may later want to father children.