הוא לא אוהב להתגלח כשהזקן שלו עוד קצר.

Because להתגלח means to shave oneself / to shave in the usual personal sense.

• להתגלח is a reflexive form: the subject is doing the shaving to himself.
• לגלח usually means to shave someone or something else.

So:

• הוא אוהב להתגלח = He likes to shave
• הספר מגלח אותו = The barber shaves him

In this sentence, since he is the one shaving, להתגלח is the natural choice.

כשה־ means when.

It is a short, very common form of כאשר or כש־, and it attaches directly to the next word:

• כשהזקן שלו עוד קצר = when his beard is still short

So the sentence structure is:

• הוא לא אוהב להתגלח = He doesn’t like to shave
• כשהזקן שלו עוד קצר = when his beard is still short

Because in Hebrew, the verb to be is usually not expressed in the present tense.

So Hebrew often says things like:

• הוא עייף = He is tired
• הבית גדול = The house is big
• הזקן שלו עוד קצר = His beard is still short

In past or future, Hebrew does use forms of to be:

• הזקן שלו היה קצר = His beard was short
• הזקן שלו יהיה קצר = His beard will be short

Here עוד means still.

That is a very common use of עוד, especially before an adjective or a state:

• עוד קצר = still short
• עוד פתוח = still open
• עוד מוקדם = still early

You are right that עוד can also mean more / another in other contexts:

• עוד קפה = more coffee
• עוד ספר = another book

So the exact meaning depends on context. In this sentence, still is the right interpretation.

Yes. You could say:

• הוא לא אוהב להתגלח כשהזקן שלו עדיין קצר

That also means He doesn’t like to shave when his beard is still short.

The difference is mostly one of style and feel:

• עוד is very common and natural in everyday Hebrew
• עדיין is also common, and can sound a bit more explicitly like still

Both are correct here.

Because קצר agrees with זקן, and זקן meaning beard is masculine singular.

In Hebrew, adjectives agree with the noun in gender and number.

So:

• זקן קצר = a short beard
• שערה קצרה = a short hair
• שערים קצרים = short hairs

Here:

• הזקן = masculine singular
• so the adjective is קצר

Yes, זקן can be confusing because the same unpointed spelling can refer to different words.

Without vowel marks, זקן can represent:

• beard
• old / elderly
• sometimes old man / elder, depending on context

In this sentence, it clearly means beard, because:

• his beard is still short makes sense
• his old man is still short does not

So context tells you which meaning is intended.

This is the normal possessive structure with של:

• הזקן שלו = his beard
• literally: the beard of him

This is very common in Modern Hebrew.

A more compact version also exists:

• זקנו

That also means his beard, but it is more formal, literary, or biblical in feel. In everyday speech, הזקן שלו is much more common.

Also, the ה־ is important here. הזקן שלו means his beard, a specific one. Without ה־, זקן שלו would sound more like a beard of his, which is not what is meant here.

In Hebrew, אוהב + infinitive often means like to do something, not only love in a strong emotional sense.

So:

• הוא אוהב לקרוא = He likes to read
• היא אוהבת לשיר = She likes to sing
• הוא לא אוהב להתגלח = He doesn’t like to shave

So לא אוהב here is best understood as doesn’t like, not necessarily hates.

The clause order is flexible.

The original sentence:

• הוא לא אוהב להתגלח כשהזקן שלו עוד קצר

is completely natural.

But you could also say:

• כשהזקן שלו עוד קצר, הוא לא אוהב להתגלח

That means the same thing: When his beard is still short, he doesn’t like to shave.

The original version starts with the main idea first: He doesn’t like to shave...
The alternative starts with the time condition first: When his beard is still short...