I had a girl with elevated liver enzymes for years, they became progressively worse despite ursodiol and liver vitamin supplements, denamarin was one. She seemed ok for a long time and never really had symptoms.
We had many blood tests, a Cushing test, three ultrasounds. Everything came back that her liver looked good, just the high enzymes from 7yrs old or so. At 11 they went up to around 1,000 so we took another ultrasound and they said her liver looked great.
She passed at 12 after developing serious neurological issues where she had basically lost her mind and was obviously in a lot of pain. The vet said either a brain tumor or because high liver enzymes degrade the brain over time. We didn’t want an autopsy, so we will never know.
At 13+ you are in a different boat, so if it were me, I would feed supplements etc and see how the ultrasound looks.