You got it! It's to put you down.
Years ago, I submitted a suggestion for improvement in job XYZ because... well... they were encouraging employees to submit ways of improving work. The manager told me that there was no time to do what I was suggesting. Three weeks later, she took credit for my idea.
As for me, I either have to ignore it or keep moving to a place where I am valued.
On that note... I have made my own decisions in life and, although not all worked out, am glad I went with what I wanted to do rather than what people were expecting of me. So, if you have an idea, and someone ignores it or disrespects you, keep moving. That's on them and not on you.
You mention age gap, and while I agree, I also consider sex is another way to put down people.
I was told I would never amount to anything

Consider the source of these comments.... are they from people you want to be like or would take serious advice from because they lead such wonderful lives? I bet you not