Are backlight issues normal on 5 year old tvs?

Hi there. My 55S423 tv suddenly became very dark, like half the brightness just went away. After researching and talking with TCL support, it sounds like it's backlight issue.

Currently, we don't have the budget for a new tv, but this exact model appeared on our used marketplace for a decent price.

My question is- is my problem common at this age, and buying the same model would be fruitless, or was mine a fluke and the same model ought to last a few more years?

Thanks!