Explanation:

- Option 1: be proved

- This is correct. Under Section 90 of the Indian Evidence Act, a document that is 30 years old is presumed to be genuine if produced from proper custody. This helps in proving the possession or ownership of property by ancestors like grandfather.

- Option 2: not to be proved

- This is incorrect. Age-old documents can indeed help prove such facts.

- Option 3: be proved at the option of plaintiff

- This is misleading. The law applies to all parties, not just the plaintiff.

- Option 4: be proved at the option of defendant

- Same as above, it's not just at the defendant's option but depends on who produces the document.