The main purpose of ads isn’t to sell you a specific product immediately, their real purpose is to expose you to their brand to make the brand more familiar (and therefore more trustworthy) to you.
For example, recently, I needed a new insurance. So of course I went to the websites of the 5 insurance companies that I knew from advertising and compared their offers. Then I went to a comparison portal, which again I knew from the ads. The best offer was from a brand I didn’t know so I went with the second one which was from a well known brand. I trusted the second offer more, simply because the brand felt more familiar to me.
Here’s another story: there is this big online clothing store. I always hated their ads, they were really annoying, and at that time I didn’t understand why anyone would buy clothes online. So guess where I went, 5 years later, after a disappointing offline shopping tour, in desparate need for new clothes?
Drawing the line is easy: Can the procedure be delayed without any life long consequences? If yes, you can wait until you’re an adult.
You want bigger boobs? That’s fine, but in the end, it doesn’t make a difference whether you do it as a 14 years or as an adult. You can wait 4 more years.
You want steroids to achieve a more muscular body? That’s your choice, but it won’t harm you to wait another few years, you will still have enough time to achieve and enjoy your ideal body when you are an adult.
You don’t want to undergo male puperty? Okay, time to act now, because you will suffer irreversable consequences if we do nothing.