十

Buddhism

limitless time and space

lost decade (esp. of Japan, 1992-2002); decade of economic stagnation

green cross (safety symbol)

kanji "twenty legs" radical (radical 55)

carbon-14

Proverb; Abbreviation

even homely girls look beautiful at the peak of their youth

Mathematics

sexagesimal; base 60

Chemistry

cesium-137; caesium-137

Idiomatic expression

beginning to learn (something) when one is old; not being too old to learn

Astronomy

Crux (constellation)

soba eaten at the end of the month (esp. at the end of the year)

Mathematics

icosahedron

twenty questions (game)

Septuagint

age seventy; one's seventies

lost twenty years; first two decades of economic stagnation in Japan that began ca. 1991

Seishun 18 ticket; seasonally available railway ticket for 5 days of unlimited travel on non-Shinkansen JR trains

jubilee; semicentennial

Music

32nd note; demisemiquaver

age eighty; one's eighties

From Confucius

at age fifty, one comes to know the will of Heaven

From Confucius

at age forty, one has no doubts

one metropolis (Tokyo), one "circuit" (Hokkaido), two urban prefectures (Osaka and Kyoto) and 43 prefectures proper; prefectures of Japan

Buddhism

the thirty guardian deities (one for each day of the lunar month)