Wii U is first console to launch with a game rated for adults only

[Soundwave]

The "timeline" of the Nintendo kiddy thing goes back a ways actually, lol, but I'll start it like this

1985- Nintendo introduces Super Mario Bros., in the successive five years the NES/Famicom becomes a global phenomenon.

1990 - Mario effectively eclipses Mickey Mouse as the most popular "mascot" character in the world.

1991 - With Nintendo owning 90% of the game market, Sega has little choice but to try something different. They start to market the Genesis towards teenagers rather than younger boys. This aggressive style of MTV marketing works, and the Genesis gains traction.

1993 - The SNES backed by Street Fighter II and many big Nintendo exclusives is starting to overtake the Genesis, but Nintendo makes a crucial mistake ... they choose to censor the arcade blockbuster Mortal Kombat. The Genesis version consequently sells much better. The "kiddy image" is basically born here.

1994 - Nintendo nixes the SNES CD-ROM behind closed doors and opts to make the N64 (then known as Project: Reality) cart based. This is really where the "kiddie" stigma gained traction. Going cart-only forced an exodus of most of Nintendo's third party support. Without franchises like Contra, Final Fantasy, Metal Gear ... suddenly Nintendo's library indeed looks more kid-skewed, because you're left with Nintendo IP primarily.

1995 - Sony enters the game industry and markets/sells the Playstation as a brand for the 20-something male player. They are "gifted" the perfect killer app for their platform due to cartridge developer exodus away from Nintendo -- Final Fantasy VII, which they market like a movie. It works and the Playstation brand largely dominates the console market for the next 10 years focusing on male teenager/college-aged players. 

1997 - Nintendo scores a surprise blockbuster hit with GoldenEye. With the James Bond character relevant now to a whole new generation. This is Nintendo's actual biggest success with this "hardcore gamer" crowd. Nintendo opts to listen to Martin Hollis of Rare and not renew the Bond license, even despite the incredible success of the game. They follow up with Perfect Dark, but Joanna Dark is no James Bond, and the game sells less than half of GoldenEye. The mantle of this game is really succeeded by Halo, which becomes the next big home console FPS franchise, unfortunately it sells XBoxes and not GameCubes. Perfect Dark on the GameCube never even materializes.

Then there was the GameCube design which was cute ... but in hindsight .... too cute for its own good (and purple as the primary color was a mistake, even Nintendo says that now they won't launch home consoles in bright colors anymore).