Assuming the car is in good shape and isn't burning oil, try the following first:
* Replace the spark plugs with OEM equivalent copper plugs gapped to factory spec. Replace the plug leads as well.

* Immediately prior to the test, get the catalytic converter as hot as possible. Set an appointment with a smog station close to a major freeway. Leave early and go take an energetic drive on the way over. Once the engine has come up to temperature, stay in the lower gears. If at all possible, include 15 mins worth of high speed freeway driving. Then roll straight off the road into the testing bay.

If that doesn't work, likely culprit is a dead catalytic converter (aka "cat"). The reactive metals that allow a catalytic converter to function degrade over time. If the original cat is still on the car, I'm not the slightest bit surprised if it's due for replacement.

By means of comparison, my Integra is 11 years old. On my last smog check in CA, I passed the 25mph HC test by one part per million. I know full well that I'll need to replace the cat before my next test. So 18 years is a damn good run.

Good luck and welcome to the board. :cheers: