I agree with many of the answers that Dave C provided. However, there could be a lot of other reasons, as well.
For example: If the distributor cap (or module) is cracked or shorted (by a carbon arc), it might cross fire (the wrong spark plug might get spark) or misfire (no spark at all at one plug).
The spark plugs might have been in for a long time. This would mean that there might be dirt built up, or that the spark gap widened. Spark plug wires might have leaky insulation? The fuel filters might be partially clogged? Broken vacuum hose?
And the list of potential problems goes on and on.
I think that you need to have a mechanic put the engine on a diagnosing machine (oscilloscope), and determine what the real problem is. Don't spent large amounts of money replacing various components until you know what is going on. However, many things (like spark plugs and plug wires) should be replaced as part of routine maintenance, and they might be near the end of their lifetimes anyway. So, it might not be a bad idea to replace a lot of cheap parts.
You can't expect a 13 year old car to run like new. Miles, engine maintenance, and even a bad driver can impact 0-60 times.
It's just old dude and won't be ask quick as new. It probably just needs a tune up or something
Manual transmission? Learn to shift quicker.
Possible plugged cat, retarded ignition timing, incorrect cam timing, dirty air or fuel filter, dragging brakes.
I have a 1999 civic si and im supposed to be getting around 7.2 seconds stock but my car is getting like 8.9 some people on youtube get 6.6 with just an intake
