My water heater runs out of hot water way faster than it used to any fixes?

It’s a 50-gallon gas water heater for a household of three. We usually get through two showers back-to-back without any issues, but lately the second shower starts going cold halfway through. Nothing else has changed in the house, and the unit is about 8 years old. Is this something that can be repaired, or is it a sign the tank is starting to fail?