Beneficiary sounds odd. I would not take his word for anything.
Beneficiary cannot administer the will himself without your consent. But if you give your consent then it is indeed ok for beneficiary to work away without you.
So, ask your self these questions:
1. Why were you named as executor? Is it only because main beneficiary was then under age but is now old enough? If so, you could bow out without in any way failing to respect the wishes of the deceased.
2. Possibly you are not too bothered about the wishes of the deceased anyway ( who should really have told you that he\she had named you as executor, by the way).
3. Is there anyone else who benefits by this will and whose interests might need to be protected? Do you have any wish to protect those interests?
One thing you cannot easily do is to start the executor's job and then decide to quit ( intermeddling as it is called).
To make an informed decision, insist on seeing a copy of the executed will, certified to you as being a true copy by the solicitor who holds it. Insist on speaking with the solicitor to ascertain why you were named as executor. Then, if you are happy to remain uninvolved, ( and feel under no moral duty to become involved) you can sign a renunciation of your executorship.