Have a portable cot that is in excellent condition the same goes for the mattress as hardly every used but it is 29 years old. Will it be safety enough for my 6 month old Granddaughter to sleep in when visiting us. Thanks

Red Nose recommends using a cot or portacot that meets the Mandatory Australian Standards. It is unlikely that these standards apply to a cot that is 29 years old.
However, you may find the information about using a second hand porta cot helpful.

If you are accepting a second hand portable cot, look for a label or sticker that says that it complies with the mandatory standard; never place baby in a cot or portable cot that does not definitely meet the current Australian safety standard.
https://rednose.org.au/article/portable-cots

Australian Standards are developed by ACCC - Product Safety.
https://www.productsafety.gov.au/products/babies-kids/kids-furniture/folding-cots

Is your cot a folding cot like the one illustrated in Red Nose article above?

Red Nose also has the following information about the use of a second hand mattress.
Any previously used mattress should have been well stored, firm and clean. If the mattress is damp, torn or mouldy
or there is any doubt about its safety, including fit, it should not be used.

Check the cot is well constructed with a good base. This includes portable cots.
The base should not sag as this may form a trough particularly with a soft foam mattress into which a baby on its tummy may roll.
https://rednose.org.au/article/second-hand-mattresses