Banking is way overrated because of the fat bonuses everyone is talking about. It is true that making a mid-career switch around 30-ish is extremely difficult due to the number of job seekers drawn to B&F industry. You wouldn't even qualify for an interview for a typical BO position that accounts for more than 50% of the vacancies in the industry.

The only way to do it in my opinion is through getting a Masters in Finance from a good university and/or taking the CFA. The former is a easier route but carries less weight while the latter is obviously harder to attain if you nuts about finance and it also requires perseverance and a lot more study time. The CFA curriculum is known to be a foot wide and a mile deep. Thus, it is highly valued in certain positions in banking and asset management industries. Should you have the determination to take on this arduous journey, I am confident you will reap the rewards in the long run.