Before analyzing this picture in full detail, I'd like to describe some of the characteristics that caught my eye right away. First of all, we notice a stick figure in the foreground, likely depicting AskedToast031; the figure's body is not centered, nor it has natural shapes. Furthermore, it has very little contrast with the gold background. The contents of the picture seem to have been depicted using only 16 colours, plus the gold in the background and some small parts in the background.
I'd like to relate this to my more childish side of me.
Often we may find ourselves in situations where we let our more immature side of ourselves take over, and thus we happen to gloss over certain details that may seem unimportant to us at the moment, but that are actually very noticeable. Furthermore, the picture clearly denotes a strong disregard for depicting reality or anything realistic, which is also a trait we used to have as small children.
Analyzing the background, we can notice two heads of a youtuber called "Skeppy", well known for its more childish side, very noticeable by his skin (a diamond derp man) and his behaviour in videos, where he loves to troll, start unfunny memes and trends, and act as a little kid. Furthermore idolatrizing a famous person is often a trait shared by very young people. Once again, the head is not shown with its natural colours, and the pixels that make it seem to have a weird texture which makes the build look noisier and messier.
One thing that has caught my eye during my analysis is the lack of detail and care put into the picture; the background appears made entirely out of the same block, and also does not contain any spots worthy of note or that break the monotony of the background. Little care has also been put into the block choice and build positioning; we can spot a water pool with ice walls peeking from behind the stick figure, which does not fit in well with gold and lime, as well as a mysterious and very likely purpose-less wooden structure at the back and a dirt house in the lower right corner.
To conclude this essay, everything I've covered here brings me to estimate the age of the author of the picture to be between 7 and 11. I've found everything to correspond perfectly with this age group, if not even younger.