You can't lie about your age to the OB, they will find that one out by looking at your medical history. Also, many doctor offices want a copy of your driver's license or state issued ID. I have been to medical offices where they refused to treat me without seeing my identification first.
You don't need to tell the OB that you used donor eggs. I never told mine, he never knew. It was never an issue. Women do get pregnant naturally at 45, I had a relative who did.