This 737-300 is at least 15 years old and maybe older. The 737-300 was built from 1979 to 1990. Again, a maintenance issue, not a design flaw.
You need to bone up on your math. 1990 was 34 years ago. I know it seems just like yesterday.
wiki:
737-300
The prototype of the -300 rolled out of the Renton plant on January 17, 1984, and first flew on February 24, 1984.[10] After it received its flight certification on November 14, 1984, USAir received the first aircraft on November 28.[1] It proved a very popular aircraft: Boeing received 252 orders in 1985, and over 1,000 throughout its production.[10] The 300 series remained in production until the last aircraft was delivered to Air New Zealand on December 17, 1999,[11] registration ZK-NGJ. By then, 1,113 Boeing 737-300s had been produced over more than 15 years.