Since Rhys had no direct contact with the whole Light and Dark mêlée, other than the Land-Rover Incident, there was nothing for him to forget, so he's basically plodded along these six years like the dutiful son he is at Clwyd farm. He had vaguely noticed a strangeness and an emptiness after Silver on the Tree but as he could not figure out the reason, he dismissed the feeling.
Nothing has changed much for him, other than a festering desire to wake up to something other than endless green hills and grey sky. His older brother, who left home the millisecond he could, sends Rhys postcards of interesting places, which are quite maddening at times.
At 26*, he is uncomplicated (relatively), friendly, shy, and good-humoured; a little old to continue formal education, and with no real want to--yet fond of books--he is still actually happy working on the farm, surrounded by what he knows and loves, which makes him feel contradictory, stuck, and rather cross for secretly wanting to widen his horizons.
[*I took the liberty of saying he was about 20 during Grey King, because 20 is still "grown-up," as it said he was, and it just sort of seemed to fit.]