This question stems from a few issues and similar meta topics.
Probably the best meta reference for this would be the question Is an asker's age relevant?; I consider this to be somewhat of a follow-up on this. This is different though, where that question and answers focused on keeping that age information in the question. This question is about only having age as the indication of knowledge level.
Basically, my question is; is the age of the asker alone enough to indicate the level of knowledge we should be answering the question at?
I'm prompted to ask this based on the (original version of) this question; where OP was asking how to explain that we can now see atoms to a 4 year old.
It's my personal opinion that in the original format, such questions would be considered opinion based. That's because we don't really know what level of physics knowledge the 4 year old has; and (as shown in the answers) users have quite different interpretations of what a 4 year old is capable of understanding. There are multiple ways to resolve this, such as by being more explicit with the level of knowledge, or by removing those restrictions completely.
It became pretty clear that many members of the community consider these questions perfectly acceptable; but I would love to have a clear consensus on this, instead of just discussion in the comments of the question.