Well, if your Dad reads this forum, my answer may screw you over, man
Your 20mw laser is going to be more dangerous than the 105 would. How do I know that ? Because anything over 5mw is dangerous to your eyesight, but since the 20mw is such a low power, you may be taking risks you might not take with a 105mw one. Does that make sense ? What you have to worry about is direct impact - sorry to disagree with you, David - but the human blink reflex, and the tendency to squint, or look away from bright things is what saves your eyesight from damage from specular reflections most of the time.
Now, to save you in case he is reading this. If you have shown responsibility with the 20mw one, and you were my child, I would let you have the 105mw without any hesitation. Here is why : If you are responsible enough to (I HATE using this analogy) handle a 22 pistol, why wouldn't you be responsible enough to handle a 44 magnum ? I really hate comparing lasers to guns - as I do not think they are weapons, but in this instance, I think that analogy is needed. You have shown to be responsible with a laser that is 4 times more powerful than what is normally described as being dangerous, so you would be just as responsible, if not MORE so with the 105mw. I owuld recommend safety goggles for you, and anyone that might be with you, when you mess around with the laser, though - because it always better to be safe than sorry. Tell your Dad to email me - he has my email addy - you do, heck, the whole board does ! I have no problems giving him ALL the facts, and then letting him decide. Whatever the outcome, man - love your Dad - he is only looking out for you.