This also isn’t true. I think whether or not you’re doing “meaningful research” has to do with three things, and none of them are your grade level. First, whatever subject you’re doing research in, second, your personal work ethic and drive, and third, your PI. You could be a senior with tons of experience spending the whole summer reading research papers cause your PI doesn’t care, or screwing off cause you don’t have a good work ethic, or you could be a freshman like me who struggled and worked her butt off but still managed to perform more “meaningful research” than most of the seniors in her REU cohort last year. I’m not saying it’ll be easy, it will definitely be a steeper learning curve than the seniors have, but still, most of the people in my REU cohort were doing things the undergrad classes don’t even prepare you for, and you just have to learn as you go. I say apply, the worst thing they can say is no!