Game like fallout but rated teen?

im 15 and my bro has fallout 3 and new vegas and i watch him play it sometimes and it would be a perfect game for me cause i want a game like that where its exploration/shooting and has quests but after you finish the quests you still have stuff to do weither its kill or explore. I ask my bro if i could play it and since its rated m he told me to ask our mom and dad first so i did. and my mom said no. I want a game like it but is rated t. Please someone know a game like it?