Mustum recens puellae dulcius videtur quam vinum vetus.

The subject is mustum recens.

• mustum = must, new wine, or fresh grape juice
• recens = fresh

So the thing that seems sweeter is fresh must.

You can tell it is the subject because:

• mustum is nominative singular neuter
• the verb videtur is 3rd person singular, agreeing with that singular subject
• dulcius is also neuter singular, matching mustum

Because with videtur meaning seems, Latin often uses the dative of the person to whom something seems.

So:

• puellae = to the girl
• literally: Fresh must seems sweeter to the girl than old wine

This is very common with verbs like videtur:

• mihi videtur = it seems to me
• tibi videtur = it seems to you

Even though puellae could also be genitive singular or nominative plural in form, here the sentence structure clearly makes it dative singular.

Because mustum is neuter singular, and the comparative adjective must agree with it.

The comparative of dulcis is:

• masculine/feminine nominative singular: dulcior
• neuter nominative singular: dulcius

Since mustum is neuter, Latin uses dulcius.

So:

• vinum dulce = sweet wine
• vinum dulcius = sweeter wine or wine is sweeter

Videtur is the passive form of video, which usually means I see. But in Latin, the passive videtur often means:

• is seen
• and from that, idiomatically, seems or appears

So here dulcius videtur means seems sweeter.

This is a very normal Latin usage:

• Marcus bonus videtur = Marcus seems good
• hoc mihi verum videtur = this seems true to me

This is the comparison: than old wine.

Latin often compares things with:

• a comparative adjective, here dulcius = sweeter
• plus quam = than

So:

• dulcius ... quam vinum vetus = sweeter than old wine

The full sense is:

• Fresh must seems sweeter to the girl than old wine [does].

Latin does not need to repeat the verb in the second part.

Because after quam, Latin normally puts the second item of comparison in the same case as the first.

Here the first item is mustum recens, which is nominative, so the second item is also nominative:

• mustum recens
• quam vinum vetus

Latin also has another way to compare things: the ablative of comparison, but that is used without quam.

So Latin could compare in two ways:

• dulcius quam vinum vetus = sweeter than old wine
• dulcius vino vetere = sweeter than old wine

This sentence uses the quam construction.

Because Latin word order is much freer than English word order.

Both of these mean the same thing:

• mustum recens
• recens mustum

And both of these mean the same thing:

• vinum vetus
• vetus vinum

Adjectives in Latin can come before or after the noun. Their endings, not their position, show which noun they go with.

In this sentence, the order is perfectly natural and may help the comparison sound balanced:

• mustum recens
• vinum vetus

Yes. They are third-declension adjectives, not first/second-declension adjectives like bonus, bona, bonum.

That is why their forms may look unfamiliar.

For example:

• recens = fresh, recent
• vetus = old

They still agree with their nouns in gender, number, and case, but they do so with third-declension endings.

In this sentence:

• recens agrees with mustum: nominative singular neuter
• vetus agrees with vinum: nominative singular neuter

Not exactly in the same sense as vinum.

• vinum is ordinary wine
• mustum is must, meaning freshly pressed grape juice, or very new wine before full fermentation

So the sentence contrasts:

• fresh must with
• old wine

That contrast helps explain why recens and vetus are used.

Yes. A more literal version would be:

• Fresh must seems sweeter to the girl than old wine

A very literal word-for-word guide would be:

• Mustum recens = fresh must
• puellae = to the girl
• dulcius = sweeter
• videtur = seems
• quam vinum vetus = than old wine

English usually prefers a slightly smoother order, but the Latin structure is straightforward once you identify the subject, dative, comparative, and verb.

Because dulcius is part of the main statement with videtur:

• mustum recens ... dulcius videtur = fresh must seems sweeter

Then quam vinum vetus is the second half of the comparison:

• than old wine

So dulcius is predicated of mustum, not directly of vinum.

In other words, the sentence is not saying:

• fresh must and old wine are both sweeter

It is saying:

• fresh must seems sweeter than old wine

Yes: Latin often puts the most important relationship in a spread-out pattern rather than in a rigid English-style order.

Here the core structure is:

• mustum recens — subject
• puellae — dative of reference
• dulcius — comparative predicate adjective
• videtur — verb
• quam vinum vetus — comparison

English learners sometimes want to read Latin left to right exactly as English, but it is better to group by function:

1. identify the subject: mustum recens
2. identify the verb: videtur
3. identify who experiences the seeming: puellae
4. identify the comparison: dulcius ... quam vinum vetus

That approach makes the sentence much easier to understand.