"Menjadi tua itu pasti."

Translation: Becoming old is certain.

[Ms.Fixer]

"Inevitable" is more natural than "certain" in this context. According to one of my dictionaries, "pasti jadi" is translated as "inevitable".

[naomileenhouts]

To become old is certain - marked wrong. Why?

[Keith_APP]

Why there is "itu"?

[KamoSaru]

It is equivalent to "is" here.

[Diponegoro57]

I think that 'itu' is used in this sentence to indicate that we are talking about the generality of becoming old, applying to everyone rather than a specific person or instance.
I could be wrong, but I would never use 'itu' for the verb 'to be' ... after all, not only to we have 'ada' and 'adalah', but many Bahasa Indonesia translations of sentences with 'is' (etc) simply leave out that verb altogether, as, I think, in this case.

[Bev425285]

Getting old is certain.