Advice on part-time job for CS student in northern Taiwan (Preferably Taipei)

Yea, COBOL is very old language and still in demand, just as you said many COBOL developers are now either died or retired. But it doesn’t worth it to embark on learning it. It’s also not easy job bcz most COBOL jobs also needs very experienced dev background (very high traffic servers with time and money critical situation). Not a noob friendly position…