Each Fallout game really starts with an entirely different main character and story. Yes, there is a larger back story, but unless you are just really dead set on knowing all that, there's no reason you couldn't just jump in and go. There are some elements that would be nice to be famailir with, but you would have no issues jumping in. Fallout 4 is different than the old games in the way that it allows you to build "settlements" and there's weopon and armor crafting ala Skyrim. So aside from some of the familiar gameplay for those of that have played it over the years, it's a new experience for everyone.
I would suggest checking out some of the "Fallout Lore" videos on YouTube that would get you up to speed on the back story a bit, but this game starts with sort of a "prequel" in the beginning anyway, showing you what life was like in this world prior to the nuclear Armageddon that made the Fallout universe what it is.
It really is a game that you would enjoy, and because it's a "sandbox" style game, there's no real right or wrong way to play it. I had a buddy come over yesterday morning and he played some of my character for about an hour and was HOOKED. And he hasn't really played any video games in about 10 years as well. But he did fine and didn't have too many issues figuring it out and getting through some of the encounters.
Word of warning: it's 5:30 am and I have been at it since last night at about 10 lol. I don't work today and my wife is going to Tulsa for an appt. so I am going to sleep all morning and wake up and start hammering it again lol. It's ADDICTING...
