I don't know as to when/how this change may have occured, but I do know that in German this is how numbers such as '26', '51', '36', etc. are phrased. IIRC '26' in German is 'sechundzwanzig' (sech-und-zwanzig) which in English is literally 'six-and-twenty'. So this phrasing could be a hold-out from the English language's Germanic origins. Anyone better informed than I please feel free to step-in and correct me!