In the 80s and 90s, video games were considered by most people to be little more than electronic toys intended for children and teens, and just like other toys it was expected that we would grow out of them by our 20s. Instead, the video game industry expanded and started making games aimed at adults. Cartoon sprites like Mario and Sonic evolved into photo-realistic characters with personalities that you can form an emotional connection with. Pixelated fantasy worlds evolved into highly immersive 3D environments with incredible levels of detail. Short and silly text dumps evolved into interesting stories that can engross the player just as well as a TV show. Video games still have a ways to go before they can claim to be as mature as some other forms of popular media, but they've long since stopped being toys intended for children.
But to those who don't follow video games, many still view them as toys that we should grow out of, and the fact that we didn't suggests to them that we're immature man-children. (No offence ladies, but the preconception of most people is that gamers are male.)