I would just give your opinion politely and i am sure the person would listen to you especially if you explained you are experienced-i know i would............
I would definitely have listened to you and I'll be 48 next birthday. It wouldn't be the first time I listened to a young person either - knowledge tends to speak for itself and be quite obvious about 30 seconds into the conversation. Tell her that you've kept fish for some time and then say it what you wanted to say exactly as you were thinking it.
I'm sure you'll gain confidence after the first time! After all, you're not exactly ignored here, are you?