Started with topical Minoxidil at age 21. Have (almost) a full head of hair. Now I take it in pill form.
No breasts. And no other issues.
Minoxidil is a sledgehammer: it's got all sorts of other effects (e.g. reducing your blood pressure, beta something something). I wouldn't expect it to cause breast development, though, since it doesn't act on œstrogen receptors.