There is so much literature about steroids and juniors. It's universal, stretching over many decades, and it's fairly well-studied and described.
As More Strides than Rides said (good post, btw), you're really gonna need to delimit your topic.
As for blood boosting, it is documented for juniors and u23s who've become (or aimed to become) pro's or Olympic champions. Some proven cases, some rumors, and some strongly implied cases:
Danny Van Haute came in contact with blood doping as a junior on the US junior team in 1974:
viewtopic.php?p=1907797#p1907797
Fritz Hagerman, OTC physiologist in the late 70s, implied/hinted at the need for blood boosting experimentation on adolescents in an article on cardiorespiratory conditioning from 1976:
viewtopic.php?p=1917825#p1917825
OTC co-founder Irving Dardik publicly stated the need for blood doping and, although he didn't say it, we know he was focusing on juniors, as the whole OTC setup was focused on finding junior talents.
Eddie Borysewicz, co-organizer of the 84 blood doping scheme, worked mainly with juniors, both in Poland (73-75) and in the US (78-85) (before he became involved in pro-cycling of course). Unsurprisingly, some (if not most) of the LA 84 blood dopers were u23.
From what I've read and FWIW, I'm convinced talented juniors were being blood doped at quite a large scale in the 70s and 80s in countries such as Germany (East and West), US, Sweden, Canada, Poland and Russia.
Two 16 year olds who got popped then admitted to EPO are Michiel van Staden in 2005:
viewtopic.php?p=1853617#p1853617
and more recently (2015) that british junior time trial champion Gabriel Evans:
http://www.cyclingweekly.co.uk/news/latest-news/junior-time-trial-champion-gabriel-evans-admits-epo-use-203450
On twitter recently, a credible twitterer (who's name is not important here) said he'd heard first hand that Sky's Dario Cioni was doping with EPO as a 16 year old mountain biker.
That,s all mainly cycling related, and USOTC.
There is probably much more to find about this if you look into other sports, marathon, skiing, and the history of bloc country doping, a.o.