Elderly chin advice

Hello! I'm technically a first time owner as Tribble is the first chinchilla we got, with another at the same time who was 2 months younger (Scrat). Scrat unfortunately passed back in 2017 in her sleep. Now, Tribble is set to be 18 this April and we were not anticipating her to still be going so strong! I know cats hide their illnesses/injuries but we've never had a chinchilla so old. What would we look for in terms of major declines in quality of life? She seems great now but I don't want her to be suffering if she does decline and I'm not aware since she is our first elderly chin. I attempted to reach out to the breeder we got them from on Instagram with no response but I can probably dig up her email if I really needed it. Thank you for any help!

Hello! I'm technically a first time owner as Tribble is the first chinchilla we got, with another at the same time who was 2 months younger (Scrat). Scrat unfortunately passed back in 2017 in her sleep. Now, Tribble is set to be 18 this April and we were not anticipating her to still be going so strong! I know cats hide their illnesses/injuries but we've never had a chinchilla so old. What would we look for in terms of major declines in quality of life? She seems great now but I don't want her to be suffering if she does decline and I'm not aware since she is our first elderly chin. I attempted to reach out to the breeder we got them from on Instagram with no response but I can probably dig up her email if I really needed it. Thank you for any help!