Obi-Wan is 25 in the TPM shooting script, though you're right about him having originally been 30 or so (back when he was the star of the movie and "Quigon Jinn" only showed up in the third act).
So "officially" Obi-Wan is only 57 when ANH begins. Kind of understandable given Ewan McGregor's relatively youthful appearance, but it doesn't quite gel with the timeframe of the OOT.