Where does “kuusikymmenvuotias” come from?

kuusikymmenvuotias (Finnish) comes from Finnish kuusi, from Proto-Finnic kuuci, from Proto-Uralic kutte — ridge; six.

Ancestry of “kuusikymmenvuotias”, step by step

kuusikymmenvuotias traces back through two separate lines of ancestry.

via Finnish kuusi

StepLanguageWordMeaning
1Finnishkuusisix; spruce; Norway spruce, "Picea abies"
2Proto-Finnickuucisix
3Proto-Uralickutteridge; six

via Finnish kymmen

StepLanguageWordMeaning
1Finnishkymmenten; decade
2Proto-Finnickümmenten; decade, group of ten
Every word from Proto-Uralic kutte →Every word from Proto-Finnic kuuci →Every word from Finnish kuusi →