There's nothing wrong with enjoying something that's immature or juvenile. One of my favorite pasttimes is drawing stupid shit for my own amusement, like this, for example!!
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I'd say it only becomes an issue if said juvenile stuff starts becoming your identity and gets in the way of a broader appreciation for things in life. Is it all you ever watch/draw/think about? It's not so much of a problem when you only draw little girls with big tits if it's simply a hobby and something you do for your own enjoyment, but if a career in art is something you're working towards, it doesn't show much in the way of versatility and can make you look single-minded and somewhat limited in creativity.
Another thing is, if you're gonna put your work out there in the public, you have to hold yourself accountable for how it's received. If you're like that dude who only draws semi-naked pictures of Princess Peach and publicly admits how someday she will leap through the Nintendo into his world and they will have a beautiful wedding and everyone on DeviantArt will be invited, then you might want to expect a few raised eyebrows. Either own up to that creepy shit and proudly make it yours, or don't share it online. Of course, showing you have a variety of interests/artistic abilities on top of wanting to draw yourself boning the Princess in Photoshop makes you seem a little less obsessed and can go a long way.
That is my story for the day, and I hope it is of some help. Also, that character is hideous, but yeah.

I'd say it only becomes an issue if said juvenile stuff starts becoming your identity and gets in the way of a broader appreciation for things in life. Is it all you ever watch/draw/think about? It's not so much of a problem when you only draw little girls with big tits if it's simply a hobby and something you do for your own enjoyment, but if a career in art is something you're working towards, it doesn't show much in the way of versatility and can make you look single-minded and somewhat limited in creativity.
Another thing is, if you're gonna put your work out there in the public, you have to hold yourself accountable for how it's received. If you're like that dude who only draws semi-naked pictures of Princess Peach and publicly admits how someday she will leap through the Nintendo into his world and they will have a beautiful wedding and everyone on DeviantArt will be invited, then you might want to expect a few raised eyebrows. Either own up to that creepy shit and proudly make it yours, or don't share it online. Of course, showing you have a variety of interests/artistic abilities on top of wanting to draw yourself boning the Princess in Photoshop makes you seem a little less obsessed and can go a long way.
That is my story for the day, and I hope it is of some help. Also, that character is hideous, but yeah.