There are few commercial aircraft that will ever reach the levels of longevity of the 737. For Airbus their A320 is 27 years old. Embraer has its E-120 Brasilia which is still flying for SkyWest (about to be retired) which first flew 32 years ago. Bombardier has its CRJ which first flew in 1991, 24 years ago.
The CRJ is often thought of as the inventor of the regional jet, however Fokker and some others would likely dispute that. However there is no doubt the Bombardier aircraft created a wave that was far more prominent than anything before. The first CRJ was a 50 seat aircraft based on a business jet design (Challenger 600) that was stretched. The initial CRJ100 was quickly eclipsed by the CRJ200 which had better engines. Amusingly, the CRJ200 was then converted back into a business jet called the Challenger 800. Because the regional jet proved so popular in the United States, Bombardier created sub variants to fit within the industry’s Scope Clause.