As far as the technical manuals of branded tyre manufacturers across the world is concerned small hairline cracks, a few or many in the sidewall or tyre edges is NOT the criteria for the tyre to be replaced.

Besides, aftermarket tyres (of traditional branded manufacturers -western and Japanese) have a specified lifespan of 10 years after manufacturing dates as embossed on all sidewalls of all tyres.

I would expect manuals ( if available in English) of Korean and some or most of China brands available locally would mention it's lifespan of 10 years.

This 3 year old tyre has a long way to go, unless it's sidewall's structure is punctured - which is about the only criteria (other than bulges) for replacement of tyres below 10 years.

Even though you didn't drive often, make sure to always pump tire air. You still can use if there is hairline cracks. But not for heavy load or long distance only city speed and continue to monitor. Worst come to worse, replace with 2nd hand tire