I've noticed that too, but I guess it's individually.
I remember when I was a child and we talked about various things, everything we said was meaningful, we sort of "spoke our minds" and when one of us talked the other knew
exactly what he meant cause we all felt the same way, there were never any misunderstandings. Then a friend of mine said "there is no meaning with anything" and everyone seemed to agree except me, and I said to them "hey, I think you took the wrong way, there is meaning to it all!" but no one agreed with me, they seemed to have closed that option and after that everything changed, we didn't understand eachother in the same way as we did before, misunderstandings could arise pretty easy. Everything they said after that was more or less meaningless we didn't feel the same connection after that.
What I think happens is that we notice a hole in our idea of meaning, a hole of meaninglessness, and if we don't fill that hole then we feel meaningless (and trust me, that isn't a pleasant feeling), the quick and easy way of filling that hole is to accept it. "There is no meaning" cause when you accept it you don't have to go back and try to fill it with meaning so you won't have to feel that meaningless again. The experiance that we have of meaningless as adults are less painful than the feeling that we experiance as children, not because we have grown up, but because we have learned to accept it (more or less).
However, I feel that accepting meaninglessness isn't the right way, cause even if the hole is very big, and it takes alot of time to find the meanings to cover the hole, it's worth it. Cause as I see it, in each step we have a limited number of ways to get to the truth, so we can either choose to look at the truth with meaning, or the meaningless truth. There's no way to tell beforehand which one is the correct truth (cause there can only be one truth), but I trust the truth with meaning to be the correct one and one of the meanings of life may be to find the meanings to cover the hole. It wouldn't surprise me if the meaning of life was to find the meaning of life