What does 歳 (～sai | ～さい) mean in Japanese?

The Japanese word

何歳ですか。
nan sai desu ka.
How old is he? | How old are you?

父は母より２歳若い。
chichi wa haha yori ni sai wakai.
My father is two years younger than my mother is. | My father is two years younger than my mother.

両親は歳を取っている。
ryōshin wa toshi o totte iru.
My parents are old.

来年で何歳になりますか。
rainen de nan sai ni nari masu ka.
How old will you be next year?

母は父より２歳年下です。
haha wa chichi yori ni sai toshishita desu.
My mother is two years younger than my father.

彼女は僕より２歳年下だ。
kanojo wa boku yori ni sai toshishita da.
She is two years younger than me. | She is two years younger than I.

来年君は何歳になりますか。
rainen kun wa nan sai ni nari masu ka.
How old will you be next year?

父はまもなく４０歳になります。
chichi wa mamonaku yon zero sai ni nari masu.
My father will soon be forty years old.

彼女は多く見ても１８歳だろう。
kanojo wa ōku mi te mo ichi hachi sai daro u.
She is at most 18 years old.

妹は３歳年下で弟は４歳年下です。
imōto wa san sai toshishita de otōto wa yon sai toshishita desu.
My sister is three years younger than I and my brother is four years younger.

父は私が７歳のときに亡くなった。
chichi wa watashi ga nana sai no toki ni nakunatta.
My father died when I was seven years old.

父が死んでから五年目の歳月がたった。
chichi ga shin de kara go nen me no saigetsu ga tatta.
Five years have gone by since my father died.

百歳まで生きる人はほとんどいません。
hyaku sai made ikiru hito wa hotondo i masen.
Few people live to be 100 years old.

彼女は六歳でピアノのけいこを始めた。
kanojo wa roku sai de piano no keiko o hajime ta.
She began lessons in piano at age 6. | She began piano lessons when she was six years old.

彼女は多く見ても２０歳というところだ。
kanojo wa ōku mi te mo ni zero sai toyū tokoro da.
She's at most 20 years old.

彼女は二十歳のときに最初の子供を産んだ。
kanojo wa ni jū sai no toki ni saisho no kodomo o un da.
She gave birth to her first child at twenty years old.

９０歳以上生きることは決してまれではない。
kyū zero sai ijō ikiru koto wa kesshite mare de wa nai.
It is not rare at all to live over ninety years. | It's not all that uncommon for people to live past the age of ninety. | It's not at all rare to live to be over ninety years old.

彼女は二十歳だと言ったが、それは嘘だった。
kanojo wa ni jū sai da to itta ga, sore wa uso datta.
She said she was twenty years old, which was not true.

父が戦死していなかったら、今は６０歳を超えているのだが。
chichi ga senshi shi te i nakattara, ima wa roku zero sai o koe te iru no da ga.
If my father had not been killed in the war, he would be over sixty years old now.

	The Japanese word
	歳
	is pronounced
	～sai \| ～さい
	means
	~ years old

	Examples:
	何歳ですか。 nan sai desu ka. How old is he? \| How old are you?
	父は母より２歳若い。 chichi wa haha yori ni sai wakai. My father is two years younger than my mother is. \| My father is two years younger than my mother.
	両親は歳を取っている。 ryōshin wa toshi o totte iru. My parents are old.
	来年で何歳になりますか。 rainen de nan sai ni nari masu ka. How old will you be next year?
	母は父より２歳年下です。 haha wa chichi yori ni sai toshishita desu. My mother is two years younger than my father.
	彼女は僕より２歳年下だ。 kanojo wa boku yori ni sai toshishita da. She is two years younger than me. \| She is two years younger than I.
	来年君は何歳になりますか。 rainen kun wa nan sai ni nari masu ka. How old will you be next year?
	父はまもなく４０歳になります。 chichi wa mamonaku yon zero sai ni nari masu. My father will soon be forty years old.
	彼女は多く見ても１８歳だろう。 kanojo wa ōku mi te mo ichi hachi sai daro u. She is at most 18 years old.
	妹は３歳年下で弟は４歳年下です。 imōto wa san sai toshishita de otōto wa yon sai toshishita desu. My sister is three years younger than I and my brother is four years younger.
	父は私が７歳のときに亡くなった。 chichi wa watashi ga nana sai no toki ni nakunatta. My father died when I was seven years old.
	父が死んでから五年目の歳月がたった。 chichi ga shin de kara go nen me no saigetsu ga tatta. Five years have gone by since my father died.
	百歳まで生きる人はほとんどいません。 hyaku sai made ikiru hito wa hotondo i masen. Few people live to be 100 years old.
	彼女は六歳でピアノのけいこを始めた。 kanojo wa roku sai de piano no keiko o hajime ta. She began lessons in piano at age 6. \| She began piano lessons when she was six years old.
	彼女は多く見ても２０歳というところだ。 kanojo wa ōku mi te mo ni zero sai toyū tokoro da. She's at most 20 years old.
	彼女は二十歳のときに最初の子供を産んだ。 kanojo wa ni jū sai no toki ni saisho no kodomo o un da. She gave birth to her first child at twenty years old.
	９０歳以上生きることは決してまれではない。 kyū zero sai ijō ikiru koto wa kesshite mare de wa nai. It is not rare at all to live over ninety years. \| It's not all that uncommon for people to live past the age of ninety. \| It's not at all rare to live to be over ninety years old.
	彼女は二十歳だと言ったが、それは嘘だった。 kanojo wa ni jū sai da to itta ga, sore wa uso datta. She said she was twenty years old, which was not true.
	父が戦死していなかったら、今は６０歳を超えているのだが。 chichi ga senshi shi te i nakattara, ima wa roku zero sai o koe te iru no da ga. If my father had not been killed in the war, he would be over sixty years old now.

	Examples sourced from tatoeba.org