Sort Dictionary by Age

Accenture España needs a consistently ordered view of staff records for an internal Python utility. Given a dictionary mapping each person's name to their age, return a new dictionary ordered by age from highest to lowest.

Do not modify the original dictionary. If multiple people have the same age, preserve their original insertion order. Python dictionaries preserve insertion order, so the returned dictionary's iteration order represents the required result.

Formal Specification

Implement sort_by_age(people), where:

1. people is a dictionary with unique string names as keys and integer ages as values.
2. The function returns a new dictionary containing the same key-value pairs.
3. Entries are ordered by age in descending order.
4. Entries with equal ages retain their order from people.
5. The input dictionary itself must remain unchanged.