I give potential clients the old Dr. vs. young Dr. analogy.  Some people would rather work with someone with 25 yrs. experience, others would rather work with someone that is young, hungry, and well equiped with the latest and greatest training, education, and technology.  Get your CFP ASAP.  If you get the job with MS and IF you can make it past the first couple hurdles, you should have your CFP in 2-3 years.  It’s difficult but very rewarding if you can make it. 

You need to address this question as though it was a concern of your CLIENTS.  The stuff you mentioned was to sell YOU to YOUR MANAGER.  That won't matter NEARLY as much as selling YOU to YOUR CLIENT.

If your client had a concern about your age, how would you address it?  What would you say?

Quite honestly, if you don't have the appearance of knowledge (grey hair), then you need to have DOCUMENTED knowledge and practical experience.  You are "always" taking courses to better your knowledge.  You leverage your resources.  If you don't know the answer to a question, you will seek out the best sources for the correct answer.

Shift from "Age" to INTEGRITY and you should be able to win over your clients.

Anyone else's thoughts?

I think the answer you and others have provided are pretty good, but sounds like your concern is that it's the Sales Mgr. who you think might have more of a problem than any potential clients. 

Do you look your age?  Could people tell?  If your concern is that the Sales Mgr. himself is holding your age against you, ask him (1) why would clients think I'm any younger or less experienced than any other FA here; and (2) how does his co. suggest that other FAs whom they have hired around your age handle the query? 

It actually seems to me to be a legitimate question, but your answer seems sufficient. 

I am in the same boat, graduated last year, and am currently interviewing at ML and SB. Today in my interview with SB, the manager asked me what I thought would be my biggest hurdle, and I addressed the "age" issue up front. I told her that would be the biggest issue to overcome with some clients. I told her that I would let these clients know up front that I am young, hungry and ready to devote myself to them. I think if you build on your age issue, you can spin it to clients as a positive. Now of course, you will run into people who would never work with a younger fa, but that is life...

use it as a positive...

DHK brought up a valid point. You sold yourself to the manager and half hearted at best.  No client will be confident in hearing "I'll be able to spend more time learning the things I need to know to manage your account better" or "you can trust me because I did an internship and studied finance for four years."  However, conveying your past experience can be a plus, especially if the internship was with a firm that is reputable in the eyes of the person questioning your age. 

In order to answer the question you need to understand the person asking the question.  Some things you may want to consider when fielding a question about your age is to determine the assumptions the person asking you is making.  The more specifically you can define their assumptions, the better the response you can provide.  The first hints you may get are how they bring up the topic, what words they use, the tone of their voice, and/or their facial expressions.  Some people overlook these data rich clues.  Sometimes people will be blunt with you about why age matters, other times they will provide subtle clues.  If you want the simple answer to how to respond to a question about your age...ask a good question.  Simply, use a direct and non-threatening question such as "what hesitations do you have about my age?" 

It's my belief that good questions are a person's best offense.  Good question's provide you with great data to shape your responses and direction of the realtions as well as display to the consumer that you are attentive and care what they think/feel.

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Two suggestions:

    "I know I'm young.  But I have 100 years of firm experience backing me up.  I'm going to be around long enough to guide you through retirement."

    "You could take your money to an advisor with 300 million and because of his asset base, you won't get much attention.  Your 500k account means a lot more to me that a more veteran broker.  I'm going to do everything I can to make sure you keep those assets and grow them with me"

If your client is middle-aged or older, you can mention that you'll be managing their money through their retirement and that you won't be retiring half way through theirs. For example, if they're 55 and you're 50, you could be retiring in 15 years and your client would have to worry about finding another FA at age 70.

As for me, unfortunately, my "youthful age" hasn't been a hurdle with my clients for a long time.