I floss like once a week and I've never had any blood show up, only time my gums bleed is when I go to the dentist and they stab me with all those metal picks and stuff.
I would deffinitely say this is the sort of thing that you should start young, I know my parents never taught me to brush me teeth or floss and I didn't start till age 22 and by that time there were already little pockets in some places on my gums where food particles always end up and its a total bitch since they fill up every time you eat and you have to licke pick at them special with the tooth brush to get them. So basically start when you are a kid so you never develop any issues because its like a positive feedback loop, the worse your gums get the easier it is for food to get caught up and make them even worse. I'm not saying like mine are terrible or anything, but they ain't winning any smile awards either (its just the frotn 4 on the bottom though, all my molars and stuff barely even peek through the gums, but thoese 4 incisors are getting bad, I sorta accepted that I will probably lose them around age 50, but who knows dentistry is alot better than it used to be and they have develped alot better methods to keep people from losign their teeth, I know like my parents talk when they were kids every single person over 50 had missing teeth, and yet nobody I know that age has any teeth missing these days except when I see like a homeless dude on the street).