It's a really stupid argument to be honest. Life should be about following your hopes, dreams and joys, and if playing video games brings you joy, then it doesn't matter how old you are.
People may approach it with varying degrees of maturity, sure, but you shouldn't aim at growing up, you should be growing up as a consequence of trying to live the life you want to live. There is nothing in there about what you can and can't do, it's all about how you use the things you do in your life.







