Where to start. Rambling thoughts...
As knabe said, cancer rates have been dropping, and cure rates have been increasing, for decades, despite what the MSM would have you believe. When we have folks routinely living into their 80s-90s, instead of wearing out or dying in their 30s-40s, well, cancer is gonna get some of them. Most women will develop breast cancer if they live long enough; most older men will develop prostate cancer - but most of these will succumb to something other than their 'cancer'.
Early puberty? So many factors can play a role:
Photoperiod - think artificial lighting... There's a reason Thoroughbred breeders and egg producers put or keep those mares and hens under artificial lighting - to bring them into estrus or keep the egg production going. I suspect most youngsters these days have the lights on well past sundown.
Level of nutrition - if you need to get heifers to 65% (or whatever) of mature body weight in order to have them cycling reliably to get them bred, what effect do you think improved nutrition (or, increased caloric intake) has had on puberty, when 5th grade girls weigh 135lb (or 250!), when 40 years ago, they might not hit that 125-135 lb mark 'til they were in the 10th grade...
The level of estrogenic activity is miniscule in beef from an implanted steer. It's easily 60-100 times higher in beef from heifers/cows with intact functional ovaries. How much ground beef that the majority of our population consumes comes from cull beef & dairy cows? The majority of it! That said, however, the estrogenic activity present in beef from those intact female bovines is still far less than that found in soy, beans, cabbage, broccoli, etc.
knabe also touched on Premarin. How many of us are on municipal water systems that source their water from rivers - downstream from other towns or cities? Mine comes from the Cumberland River; I'm downstream from Nashville TN and numerous southcentral KY towns - reckon how much urine from women with active ovaries, or on birth control pills or post-menopausal hormone replacement therapy is in the water by the time it gets to Lake Barkley, where my drinking water comes from? Granted, it's diluted, and my water supplier filters and chlorinates, but what's the 'hormone' level in my drinking water? I dunno.
The concern over amount of 'hormones' in beef from implanted steers is, IMO hysterical 'straining at a gnat' - it's less than miniscule. Most, if not all of those growth-promoting implants exert their action by stimulating the pituitary gland to release more 'natural' growth hormone - resulting in an animal that produces more lean muscle mass and less fat - isn't that what the consumer keeps telling us that they want?!