Das Alter ist wichtig.

Because Alter is a neuter noun in German: das Alter.

German nouns have grammatical gender, and you have to learn each noun together with its article:

• der = masculine
• die = feminine
• das = neuter

So the correct form is always das Alter.

In German, all nouns are capitalized.

So:

• das Alter = age
• wichtig = important → not capitalized, because it is an adjective

This is one of the most noticeable spelling differences between English and German.

Ist is the 3rd person singular form of sein (to be).

The subject is das Alter, which is grammatically singular, so German uses:

• das Alter ist = age is

Compare:

• Ich bin = I am
• du bist = you are
• er/sie/es ist = he/she/it is

This is standard German main-clause word order:

Subject + verb + complement

So:

• Das Alter = subject
• ist = verb
• wichtig = predicate adjective / complement

A key German rule is that in a normal main clause, the conjugated verb comes in the second position.

Because here wichtig comes after the verb ist and describes the subject. In this position, it is a predicate adjective, and predicate adjectives do not take adjective endings in German.

So:

• Das Alter ist wichtig. = correct

But before a noun, adjectives do take endings:

• das wichtige Alter = the important age

That is why you see plain wichtig here.

It can often be understood as either the age or age, depending on context and how natural the English translation is.

German often uses the definite article where English might use no article:

• Das Alter ist wichtig. could be translated as
  • Age is important.
  • The age is important.

If the sentence is talking about age in general, English usually prefers Age is important. If a specific age is meant, English may prefer The age is important.

Normally, no. In standard German, Alter ist wichtig sounds incomplete or unnatural in this meaning.

German usually needs the article here:

• Das Alter ist wichtig.

English often says Age is important without an article, but German usually does not copy that pattern directly.

Yes. That is also grammatical.

• Das Alter ist wichtig. = neutral, standard order
• Wichtig ist das Alter. = puts extra emphasis on wichtig or sounds a bit more stylistic

In both sentences, the verb still stays in the second position, which is a very important German rule.

Yes. Alter can mean age, but in other contexts German learners may also encounter:

• alt = old (adjective)
• älter = older
• das Alter = age / old age

In your sentence, das Alter is clearly the noun age.

Be careful not to confuse:

• Das Alter ist wichtig. = Age is important.
• Er ist alt. = He is old.

A simple pronunciation guide is:

dahs AHL-ter ist VIKH-tikh

A few notes:

• Alter is stressed on the first syllable: AL-ter
• wichtig is stressed on the first syllable: WICH-tig
• the ch in wichtig is the soft German ich sound, not a hard k

If you want a smoother rhythm, say it like this:

Das AL-ter ist WICH-tig.

It is neutral and works in both formal and informal German.

There is nothing especially formal, casual, or slangy about it. It is just a plain factual statement:

• Das Alter ist wichtig.

Here is the breakdown:

• Das = definite article (the)
• Alter = noun (age)
• ist = verb, from sein (is)
• wichtig = adjective (important)

So the structure is:

article + noun + verb + adjective

Yes. This sentence pattern is very common.

For example:

• Das Alter ist egal. = Age does not matter.
• Das Alter ist entscheidend. = Age is decisive.
• Das Alter ist relevant. = Age is relevant.

The pattern is:

Das Alter ist + adjective

And the adjective still stays without an ending after ist.