I want to put these words in a sentence that makes sense.
Many will think that my voice doesn't matter for people my age.
It doesn't sound right to me.
It's fine ... or you could write, "...that people my age don't have opinions that count yet."
To put these words in a sentence that makes sense, you can try rephrasing the sentence slightly. One way to do it could be:
"People of my age often believe that my voice doesn't matter much."
This sentence conveys the idea that many individuals who are the same age as you might think that your opinion or voice doesn't hold much significance. However, feel free to make further adjustments based on your personal preferences and the context in which you intend to use the sentence.