I just found my male parakeet mating with my female conure.

[Pajarita]

Welcome to the forum. Actually, I do not think that any breeding behavior is harmful to birds. What is harmful is for a bird to be so hormonal or so confused about its identity that it wants to 'mate' with a human - not because the actual action is harmful per se but because of what it means in terms of physical and/or emotional health for the bird (meaning, for this to happen, the bird has to be overly hormonal which means their endocrine system is out of whack).

Now, personally, I would not discourage them at all. It is, after all, a perfectly natural behavior this time of the year as it is spring (I have several birds that are nesting and having sex right now). What puzzles me is your comment that your one year old GCC has already tried to masturbate on you because, at one, she is not sexually mature yet -she would be the equivalent of a tween so, although she could be a bit precocious and might have already started producing sexual hormones, they should not be present in such quantity in her bloodstream so as to provoke that behavior. Is it possible that she is actually older than one? Is she being kept at a strict solar schedule with 2 hours of exposure to dawn and dusk? Is she being fed anything with soy in it? Freefed protein food? Because the behavior you mention should not be happening at all - much less so early.