sixtyne [OE]
sixtene [MI]
sixteen [ME] 
sixtien
https://www.etymonline.com/word/sixteen#etymonline_v_24138
https://www.merriam-webster.com/dictionary/sixteen
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED40597
https://bosworthtoller.com/27910