I've been around horses all my life too, grown up on their backs practically- when I was 13, my horse was semi-retired, and so I needed a new one. I happened to find a 2 year old arabian colt, and figured, 'okay. I've ridden green horses. Horses really like me. He's young, so he'll get attached to me and we'll form an even better bond. I can sit a buck. I have a mom who's trained horses before. She can help me, and I can train my first horse.'- sound familiar?
My mom went to nursing school and is rather notorious for not keeping promises, so no help there. I realized just how much I didn't know about horses, which made me feel embarrassed, and I barely eeked by with ground work for 4 years, only recently, at 17, am I starting to really train him. It was by the grace of God that I found a 2 year old that was as calm and sweet as he is, because if he didn't have the mind he does, it would have been horrible.
I highly suggest, from my own experience, that you find a horse that isn't described as needing an experienced rider, preferably older/ done growing. Trust me, older does not equal boring or a horse with no energy... my first horse was a 6 1/2 year old quarab gelding, and he had lots of training, he was an excellent horse, but he was full of energy, and a huge challenge, but the only way I could get hurt on him was if I was stupid. If you want to challenge yourself, you can. Just make sure you're not challenging yourself too much- and I can almost guarantee you that this horse you're looking at is a much bigger challenge than you think. Please be safe, and good luck- I know there's a great horse out there for you.