GMOs have no ability to modify human DNA. The technology used to modify the plants to begin with is not present in the grown plant or the harvest itself. Sometimes a virus is used to introduce the modification to the plant seed, but it is not a virus that uses an animal host. Even if the virus/other tech used to modify the plant were present in what we ate it would not go around altering our DNA. To go all biology geek technical on the subject, most of the modifications are to increase crop yield which is accomplished in nature and the lab by increasing the number of copies of the chromosomes present. Plants work on a totally different method of evolution (GMOs and plant husbandry just speed it up) to what animals do. You can make a case for GMOs being bad due to decreasing diversity in our food supply, but modifying us, just no.
Men/boys developing breasts is mostly due to estrogen-mimicking compounds present in soy products. Some males are more susceptible to the effects at low dosages than others, possibly due to less overall testosterone to begin with, but it boils down to a diet issue. Vegans and hardcore vegetarians who use soy as a protein replacement are well documented as having issues with gynecomastia and reduced sex drive. A guy I work with (in his late 50's) decided to go mostly vegetarian a few years ago and has now started growing man boobs. Just read the labels on processed foods, at least half have some soy derivative in them. The increased estrogen could make girls hit puberty faster, but I haven't seen that in research literature yet. Most attribute it to hormones in meat.
Some products are good to buy organic to reduce pesticide exposure, some there is no benefit. It is best to read up on which instead of spending double or triple for no benefit. Keyword is organic since that is a term regulated by the FDA but isn't as organic as I would require for the label but whatever. Any other terms are buzzwords as far as any oversight is concerned.
Lactose intolerance is due to your genetic makeup. At a certain age most of the world's population loses the ability to produce lactase (breaks down lactose) so milk (especially 2% 1% and skim since they contain more lactose per unit volume) and fresh milk products will give them gastrointestinal distress. Cheese and yogurt don't because there is little to no lactose left in them. Some people will lose the ability to produce lactase if they stop drinking milk for a long period of time. Luckily you can take lactase in a pill form if you are intolerant and love ice cream.