Training seriously as in lifting/sprinting/etc with consistency? Since April of this year so, 5 months. I've always been very active, played ball, ran track, etc in HS. I never lifted though, just ran and jumped a lot but it was effective apparently.
As far as how I've been lifting since April, it's not really patterned after any particular program I just got in the gym and lifted twice a week (usually Monday and Thursday) and did some running once or twice a week as well. the lifts I focused on in particular were/are the squat, squat jump, and depth jumps/box jumps with some lunges sprinkled in. Really basic stuff. I started with a max squat of around 225lbs but was at the 300lb mark in 2-3 weeks by learning the form/getting comfortable. The 360x3 PR came last Monday and I feel like I'm still gaining but I pulled my groin Wednesday sprinting so I'm taking a week or so off. I was following Chase Skinkis (I think thats how you spell his name) and Tyler Ray on youtube and Chase in particular seems to have made some good gains using Tyler's program so I'm going to try it when I start up again. After I use that I'll probably try to structure my own thing based on the lifts/exercise I feel help me the most.
FYI the only 'problem' I had doing my own thing was that while my vert has gone up I am jumping slower it feels like. it's just not as explosive feeling. I think I lost some 'springiness' (lol) during training but I'm making up for it by being stronger. After reading on here I should probably be focusing on maintaining my strength and work on being quicker in my plant/jump.