Incumbents tend to be seriously difficult to unseat because of their political influence and power and networking within the system, and mostly about a dozen or so congressional seats are competitive out of 435 seats which is why a lot politicians can stay in office for decades.
Having younger representatives representing the much younger population who's future will be impacted the most by laws and policies as older people will be dying off not far into the future.
Moreover, the far older generations had their opportunity and era and shouldn't be impacting younger generations future by their laws and polices.
Age limit should can't run for office after age 65.