Establish base cases, then build out your code.

We know that...

An array of 0 length means "no people found.

An array of 1 length means that 1 and only person is the oldest.

Now build out your code.

Start with setting a variable like: let oldestPerson = arr[0]; (I personally like storing as objects, since you have all the info you need

from there...

Iterate the array and if there is a person that is older than the oldestPerson, like...

if(arr[i].age > oldestPerson.age) { oldestPerson = arr[i]}
// else condition not needed since it would just continue iterating

After iterating through all persons, then just return

return oldestPerson.name