Dodd-frank means that prop trading isn't really a thing the way it used to be. Most trading in banks is now flow trading: the bank will take one side of a trade for a client in exchange for a fee. They'll then make sure their book is hedged so they don't have meaningful market exposure.

Asset managers still make big, directional bets though. Exactly how decisions are made varies from place to place, but decision makers will typically be older and have plenty of experience. Asset managers get lots of due diligence questions so no-ones handing millions out to a junior in their early twenties.

With regard to entering the industry, it's pretty hierarchical, and can be siloed: techies do tech, traders do trading, and there's not much crossover.

The most reliable way of entering the industry is to get on a graduate program and work your way up. Failing that, a quantitative PhD might get a hedge fund or HFT interested.

Do be aware that while it's a ticket to a comfortable upper middle class life, the salaries are not what they once were. Seven-figure bonuses are pretty much a thing of the past for most front office staff.