El plátano está maduro.

Because maduro here describes a state or condition of the banana: it is ripe now. In Spanish, temporary conditions are normally expressed with estar.

So:

• está maduro = it is ripe
• es maduro would sound wrong for a banana

This is also a useful contrast with people:

• Es maduro = he/she is mature
• Está maduro = he/she seems ripe/ready in some literal or unusual sense, not the normal meaning

For fruit, estar is the natural verb:

• La manzana está verde = The apple is unripe
• La pera está madura = The pear is ripe

Because plátano is a masculine noun in Spanish, so it takes the masculine singular article el.

• el plátano
• el mango
• el melón

If the noun were feminine, you would use la:

• la manzana
• la pera

There is no special logical reason why plátano is masculine; that is simply its grammatical gender, which you learn with the noun.

The accent mark shows where the stress goes: PLÁ-ta-no.

Without the written accent, Spanish spelling rules would make you stress it differently. The accent tells you clearly that the stress falls on the first syllable.

So the pronunciation is roughly:

• PLAH-ta-no

This written accent is part of the correct spelling, so it should not be omitted in careful writing.

In Spanish, descriptive adjectives often come after the noun.

So:

• el plátano maduro = the ripe banana
• la fruta fresca = the fresh fruit

That is the most normal position here. In your sentence, maduro is not directly inside a noun phrase like the ripe banana; it is part of the predicate after the verb:

• El plátano está maduro

That structure is very common:

• El café está caliente
• La sopa está fría

Because maduro has to agree with plátano, which is masculine singular.

Agreement rules:

• masculine singular: maduro
• feminine singular: madura
• masculine plural: maduros
• feminine plural: maduras

Examples:

• El plátano está maduro
• La banana está madura
• Los plátanos están maduros
• Las peras están maduras

Yes, it can mean both, depending on context.

With fruit, maduro usually means ripe:

• El tomate está maduro = The tomato is ripe

With people, maduro often means mature:

• Es una persona madura = He/She is a mature person

So the word is the same, but the English translation changes according to context.

In Spain, plátano is the usual everyday word for banana.

You may also hear banana, but in Spain plátano is the more standard and common choice in many contexts. In some places, people may use the two words with slightly different nuances, sometimes referring to different varieties, but for a learner of Spanish from Spain, plátano is the safest and most natural word to know first.

So if you want to say banana in Spain, plátano is a very good choice.

Normally, it refers to a specific banana: the banana is ripe.

The article el often points to a particular banana that both speaker and listener can identify, for example one on the table.

If you wanted to speak more generally, Spanish could use other structures depending on the context, such as:

• Los plátanos están maduros = The bananas are ripe
• Un plátano maduro = A ripe banana

So this sentence is most naturally understood as referring to one particular banana.

No, not in normal Spanish.

With a singular countable noun like plátano, you usually need an article or another determiner:

• El plátano está maduro
• Un plátano está maduro
• Este plátano está maduro
• Mi plátano está maduro

Saying Plátano está maduro sounds incomplete and unnatural.

You change the noun, the verb, the article, and the adjective so they all agree:

• El plátano está maduro = The banana is ripe
• Los plátanos están maduros = The bananas are ripe

Changes:

• el → los
• plátano → plátanos
• está → están
• maduro → maduros

This kind of agreement is very important in Spanish.

It is pronounced roughly es-TAH, with the stress on the second syllable.

A few helpful points:

• the written accent in está shows the stress
• the e is a clear short vowel, like eh
• the a is an open ah sound

So:

• está = es-TAH

In normal everyday Spanish, no. For fruit being ripe, Spanish uses estar, not ser.

If you want to describe a type or characteristic, you would usually express it differently, not with ser maduro:

• Es un plátano muy dulce = It is a very sweet banana
• Es un plátano de Canarias = It is a banana from the Canary Islands

But for the condition ripe, use:

• El plátano está maduro

Not if you specifically mean ripe.

For fruit, the common word is maduro. The opposite is often verde when the fruit is still unripe.

Examples:

• El plátano está verde = The banana is unripe / not ripe yet
• El plátano está maduro = The banana is ripe

Listo means things like ready, clever, or done, so it would not be the normal choice for fruit.

Because Spanish often does not need an explicit subject pronoun.

In English, you must say:

• It is ripe

In Spanish, the subject can be a noun:

• El plátano está maduro

And if the context is already clear, Spanish can even omit the noun and just say:

• Está maduro = It is ripe

Spanish verbs carry information about person and number, so subject pronouns are often unnecessary unless you want emphasis or contrast.