Would like to get a corn snake.

[zakocsm]

So, here's my problem.
When I was about 9~ I got a veiled chameleon. It was a cool pet for about 1 year, then, I decided I wasn't going to take care of it anymore and made my dad take care of it for the rest of its couple of years. I will admit, the only, only reason I did not take care for it for the rest of its life was because I was afraid of the crickets. I hated the crickets, and also it got very aggressive towards me for who knows why. Now, I have two African dwarf frogs and a beautiful female beta in a 5 gallon tank, but they won't let me get anything bigger than that, and I can see why. They don't trust me anymore, and I very much regret doing that when I was nine. I am now 13 and I am a lot more responsible then I was back when I was 9, I am a lot smarter, I know how to do research, and overall I think I can take care of a corn snake or ball python. But, like I said, they don't trust me. How should I approach this? Also, could I have some general information on them, just for verification? Like max size they get, max terrarium size I may need, and things like that.
More background information if you care at all: Another reason for the no trust at all when it comes to pets is because of my sister. When my sister was a bit younger, 11ish, she got 2 African chichlids and a plecostomus in a 10 gal tank. After about 6 months, she completely just gave up in it because she said "she honestly doesn't care about them anymore" because of her annoying "feminine teen" state she went through for like a year. She never cleaned it, and forced my mom and little sister to clean everything for no pay or anything. So, yea. Also, when I was younger, before my chameleon, I had a betta in a three gallon tank. It lived for 4 YEARS, with no heater and filter and I changed its water every week. I loved that betta, and that's why they trust me with my betta and ADF's
THANKS FOR ANY HELP, AND SORRY FOR SUCH A LONG THREAD. VERY SORRY, I LIKE TO BE THUROUGH THOUGH.