That's not a good time for an amateur, it's an insanely good time for an amateur. The world record is currently 2:03:38. A 2:30 would have put you in 22nd place (out of 26,000!) in this year's Boston Marathon.
I am not thinking of dabblers; many people will do marathons after having barely trained. The goal for these people is just to finish.
I think 2:30 is achievable for a healthy, moderately talented man who is not merely dabbling: someone who is training correctly and has put in a few years of sustained, injury-free effort.
2:30 is still very much an amateur time. For example, I think that even though 2:15 or faster is professional-caliber it is still nowhere near being competitive.
I do want to point out somewhat pedantically that it takes being in better-than-2:30 shape to run 2:30 on the Boston course, a notoriously slow course. There are runners who ran more slowly than 2:30 in Boston when they could have run 2:30 elsewhere.