There's nothing that says that particular bird-of-prey was 80-years old--there have been multiple upgraded versions or variants of the design mentioned onscreen and the Class-D12 may only have been 20 or so years old for all we know. As a 24th-Century ship, its weapons probably could have taken out the 23rd-Century Enterprise
-A even easier.
Also, it took multiple shots--not a single one--for that b.o.p. to take out the defenseless Enterprise