My DH, also 39, has been dealing with this since July. The elevated liver enzymes were an incidental finding on his life insurance physical/bloodwork. His AST, ALT, ALP, and GGT were all high, all other values normal. No symptoms, he's in decent shape, not much of a drinker BUT he was just finishing a course of Augmentin when they drew the blood and apparently that drug can affect the liver. He self-monitored the values for two months (did everyone know you can go to the lab and request any bloodwork you want if you pay OOP?) Initially, there was improvement, but after a couple of months the values plateaued, still high, and he scheduled an appointment with a hepatologist. The doctor has done an e.x.t.e.n.s.i.v.e. evaluation of my DH's liver -- an MRI with elastography, autoimmune disorder testing, DNA mutation analysis, checking for rare and exotic forms of Hepatitis that I didn't even know existed, etc. They've found nothing amiss. (And the doctor is the Director of Hepatology at one of the nation's top hospitals, so I believe he's well qualified.) So, still no answers but no scary results either.
A friend of ours also had unexplained elevated liver enzymes at one point. They rechecked her bloodwork a few months later and the values were down but still high, another recheck a few months after that and everything was normal. She never had an explanation for what may have caused it.