An interest is always the best way into study, if it doesn't interest you, you won't do so well, and it sounds like you have both interest and passion, which means you should do well.
You are still young though, so I'd try and avoid getting too specialised right now, and think a little more broadly.
Venom study would encompass a few areas; zoology, biology, chemistry, and pharmacological studies possibly.
Im not sure where you are from; but in England you'd be doing GCSEs, so study hard in your sciences, and pay keen interest to chemistry, and biology.
College will allow you to specialise further, and if your ideals are still the same as they are now, they will be able to advise you. Possibly a combined sciences, chemistry, medical sciences type course.
University will specialise still further in your areas of interest at BSc, MSci, level.
As a graduate with a BSc (bachelor of science honours degree) you would have the choice to move into industry and perhaps take a job in zoology, biology, dangerous reptiles etc, or study further. MSci, PhD etc.
You won't need to go all the way to PhD level to follow your passion for dangerous reptiles.
Maybe it's sownthing you could take up with a school careers advisor, or if they don't know, have a look at University courses relevant to that area, and see what career opportunities are offered. Then begin to aim for something you like the sound of as a start.