To be honest, before the game's release, I was a bit worried that the critical reception of the game would be overly harsh because of this kind of bias, which doesn't really mean anything, and I totally agree with you. I don't think it's wrong to say that the game is trying to appeal to a young audience, but that doesn't mean it's only aimed at them. We can judge a game on what it is, not on the image we have of it.
However, I have to admit that on reading the first feedbacks, even if we can indeed read a few reflections on the intended audience, I have the feeling that critics are going a little overboard in their indulgence, perhaps too pronounced in their desire to be benevolent. Irrespective of the audience, real or supposed, for which the game is intended, problems of performance, repetitiveness and lack of depth seem to be major flaws.
Kirby and the Forgotten Land is an absolutely adorable game, and yet I don't remember reading reviews that constantly emphasized a supposedly young audience. Perhaps that's because there was no need to even ask the question of audience to downplay or minimize obvious flaws, since it was simply an excellent game. I bought PPS because I want to play it with my nephews, but honestly I would much rather have read that the game had great variety, that the experience was getting richer as it went along and that the performance problems had disappeared since the demo than to read that all that was still there but that it didn't matter because it's cool that Peach has her game.