Pensiunan itu rentan terjatuh ketika penglihatan dan mobilitasnya berkurang.

Pensiunan means a retiree or a retired person.

It comes from pensiun meaning retirement or to retire, plus -an, which often helps form a noun. So pensiunan itu means that retiree or sometimes the retiree, depending on context.

This is more natural than saying orang pensiun.

In Indonesian, words like ini and itu usually come after the noun.

So:

• pensiunan itu = that retiree
• rumah itu = that house
• buku itu = that book

In many cases, itu can also make the noun feel definite, so pensiunan itu can mean either that retiree or the retiree, depending on the situation.

Rentan means vulnerable, susceptible, or prone.

In this sentence, rentan terjatuh means prone to falling or vulnerable to falls.

It is often used in slightly formal, medical, social, or safety-related contexts. For example:

• rentan sakit = prone to illness
• rentan cedera = vulnerable to injury
• rentan terjatuh = prone to falling

A less formal alternative might be mudah jatuh, but rentan terjatuh sounds more formal and clinical.

Jatuh simply means to fall.

Terjatuh usually adds the idea that the fall is accidental or unintentional. The prefix ter- often gives that kind of meaning.

So:

• jatuh = fall
• terjatuh = fall accidentally / end up falling

In a sentence about physical risk, terjatuh is very natural because it highlights accidental falls, which is exactly the kind of problem being described.

Both can be understood, but rentan terjatuh sounds more natural in a health or safety context because it emphasizes accidental falling.

• rentan jatuh = prone to fall
• rentan terjatuh = prone to accidentally falling

Since older adults are usually not choosing to fall, terjatuh fits the meaning well.

Ketika means when.

Yes, you can often replace it with words like:

• saat = when
• waktu = when
• pas = when, at the time that, more informal

So these are all possible:

• ketika penglihatan dan mobilitasnya berkurang
• saat penglihatan dan mobilitasnya berkurang
• waktu penglihatan dan mobilitasnya berkurang

Ketika sounds a bit more formal or written than pas.

Penglihatan means vision or eyesight.

It is related to the root lihat, which means to see.

A helpful comparison:

• lihat = see
• melihat = to see
• penglihatan = sight, vision, eyesight

The pattern peng- ... -an often forms nouns related to an action or faculty.

Here, -nya means his/her or their, depending on context. In this sentence, it refers to the retiree.

So mobilitasnya means his/her mobility.

Important point: -nya does not tell you gender. It can mean:

• his
• her
• its
• their

depending on the context.

Yes, in this sentence it is understood to apply to both: the retiree’s vision and mobility.

So penglihatan dan mobilitasnya is understood as:

• his/her vision and mobility

Indonesian often does this in coordinated phrases. It does not always repeat the possessive marker on both nouns.

A more explicit version would be:

• penglihatannya dan mobilitasnya

But the original sentence is normal and natural.

Berkurang means to decrease, to decline, or to become less.

It is intransitive, meaning the thing itself becomes reduced.

So:

• penglihatan berkurang = vision declines
• mobilitas berkurang = mobility decreases

By contrast, dikurangi means is reduced by someone or something. It is passive and usually suggests an outside agent.

For example:

• Anggarannya dikurangi = The budget was reduced
• Penglihatan berkurang = Vision declines

In this sentence, berkurang is the natural choice because the retiree’s vision and mobility are declining, not being actively reduced by a person.

Yes. Indonesian allows this kind of time clause to come before or after the main clause.

Original:

• Pensiunan itu rentan terjatuh ketika penglihatan dan mobilitasnya berkurang.

Also natural:

• Ketika penglihatan dan mobilitasnya berkurang, pensiunan itu rentan terjatuh.

The meaning stays basically the same. Putting the ketika clause first gives a little more focus to the condition.

Yes, it is natural, especially in a formal, educational, medical, or safety-related context.

A small nuance: pensiunan specifically means retiree, not just an elderly person. So if the idea is about older adults in general, Indonesian might also use:

• lansia = elderly person, senior
• orang lanjut usia = older adult, elderly person

But if the topic really is retired people, pensiunan is perfectly fine.