1A year — the calendar unit, also used to refer to specific years (this year, last year, next year). The kanji 年 is read とし in standalone noun use and native compounds (今年 ことし, 年の暮れ, お年玉), but ねん when paired with a number (三年, 令和5年).
今年(ことし)はあっという間に過ぎた一年だった。
This year felt like a year that flew by in an instant.
年の暮れには毎年大掃除をする。
Every year at year-end we do a big cleaning.
あの年の夏は本当に暑かった。
The summer of that year was really hot.
良い年をお迎えください。
Wishing you a good year ahead. (a common year-end greeting)
2Age — how many years old someone or something is. Used in expressions like 年は？ ("How old are you?") or 年を聞く ("to ask someone's age"). When a specific number is given (e.g., 30歳), the kanji 歳 is used; 年 covers the abstract notion of age.
失礼ですが、お年はおいくつですか。
Excuse me, may I ask your age?
あの俳優は年の割にずいぶん若く見える。
That actor looks remarkably young for his age.
二人は年が三つ離れた兄弟だ。
The two are brothers three years apart in age.
年を聞くのは失礼にあたる場合もある。
Asking someone's age can sometimes be considered impolite.
3Old age; being past one's prime. A somewhat indirect way to refer to the effects of aging, common in expressions like 年には勝てない ("you can't beat age / age catches up with you") and 年を感じる ("to feel one's age").
階段を上がるのもつらくなった。年には勝てないね。
Even climbing stairs has gotten hard. You really can't beat aging.
最近、白髪が増えてきて年を感じる。
I've been getting more gray hairs lately and feeling my age.
あの選手も年なのか、最近は走るスピードが落ちた。
Maybe age is catching up with that player — his running speed has dropped lately.