die Jugend
youth
The stage of life between childhood and adulthood.
In seiner Jugend war er ein leidenschaftlicher Musiker.
In his youth, he was a passionate musician.

youth
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youth
The stage of life between childhood and adulthood.
In seiner Jugend war er ein leidenschaftlicher Musiker.
In his youth, he was a passionate musician.

'Die Jugend' is the noun related to the adjective 'jung' (young). It describes the state or time in which someone is young.
Als er jung war, hatte er viele Träume.
When he was young, he had many dreams.
'Jugend' can mean a stage of life or a group of people. When it is used with a possessive pronoun, as in 'in meiner Jugend' (in my youth), it means the stage of life. When people speak generally of 'der Jugend' (the youth / young people), they often mean young people as a group.
In seiner Jugend reiste er durch die ganze Welt.
In his youth, he traveled all over the world.
To talk about your own past or another person's past, the phrase 'in meiner/deiner/seiner Jugend' (in my/your/his youth) is used very often.
Meine Großmutter erzählt oft Geschichten aus ihrer Jugend.
My grandmother often tells stories from her youth.
age
'das Alter' and 'die Jugend' can both describe stages of life, but in that case they are opposites. 'die Jugend' means the time between childhood and adulthood. As a stage of life, 'das Alter' means the later time in life, when someone is old. They can be confused because 'Alter' can also simply mean the number of years someone has lived. Then it is not a direct opposite of 'Jugend'. For example, you can ask about a person's age, whether they are young or old. As stages of life, the rule is: youth at the beginning of life, old age at the end.

In ihrer Jugend spielte Maria fast jeden Nachmittag Fußball.
In her youth, Maria played soccer almost every afternoon.
Im Alter möchte Herr Kaya in der Nähe seiner Kinder wohnen.
In old age, Mr. Kaya would like to live near his children.