First, I wouldn't personally recommend a mangrove snake until you have a lot of experience in mentoring under someone who has a lot of venomous experience. I have personally seen some gruesome side effects from bites of mangroves and they should not be taken lightly (nor should they be kept by novices w/no venomous experience....especially a 15 year old!).
Working with racers, coachwhips and various Nerodia can certainly offer "cobra-like" tendencies but they will never duplicate them (but its a good place to start learning). The important thing, no, THE most important thing (aside from living a clean and responsible life) is that you master proper technique such as mastering the use of trap boxes, moving a snake from point A to point B w/out ever touching it, etc. If you have ideas of hooking/tailing cobras like you see on Animal Planet, you may want to consider sticking with non venomous; that stuff is for T.V. only (not that hook and tail is a bad thing but it really isn't necessary). So, find someone you can mentor under; listen, learn, and develop sound and safe techniques. Humility and respect goes a long way in the venomous field.
Hope that helps....and waiting until you are at least 23 years old is already showing the maturity that it takes to successfully work with venomous herps.
Rob Carmichael, Curator
The Wildlife Discovery Center
Lake Forest, IL
>>A decent sized mangrove snake would be a good choice if you can find one.
>>
>>
-----
Rob Carmichael, Curator
The Wildlife Discovery Center at Elawa Farm
Lake Forest, IL