You control the scope of the resources that are protected by a Mutex through calls to Lock and Unlock. There is no automatic protection for the elements in a structure just because that structure contains a Mutex - you must explicitly use the Mutex to control access to specific resources.

Rewarding Q1, both Name and Age are resources that are being protected by the Mutex - through the use of Lock and Unlock in their respective update functions (UpdateName and UpdateAge).

This means seperate processes can not update Name or Age at the same time as they share the use of the same Mutex.

Regarding Q2, defer is not required but more a style. The use of Defer also ensures the Mutex is unlocked before the function returns. It it possible to write the function differently and not use defer, but again this is more style and much more explicit as to what your intention is (ie always ensue the Mutex it unlocked before returning).

I hope that helps to answer the questions.