There are so many things to worry about, Novice. For example: climate change will soon make all other worries irrelevant; Tiny Trump is attacking our democracy with help for the Russians, and the GOP is on board; and millions of people may soon lose their health insurance. Your worry? Push it so far down on the list that you never think of it again. I was a literary agent for 14 years, and I knew many agents, and I can't credit anyone turning down a first-rate writer for being too young. The agent you mentioned had some concern that young writers might not have developed the skills to be published yet--so she's talking generally about first impressions prior to read. The remedy is not to share your age in a query letter. (Why would anyone do that, anyway?!) No one is going to google the writer until and unless they've read the work and fallen hard for it. Then they will google the writer, maybe check out his/her social media presence...but it just makes no sense from an agent's perspective to refuse representation to a writer who has 50+ productive years ahead of him.
Climate change, OTOH...