I have been doing it for years and I am earning much more on this "side gig" compared to my "real job" or maybe I should call my full time job a "side gig" at this point...
edit:spelling error
1. Your mentor will never tell you a working trading strategy, instead he is going to use for himself to make money... You are his competitor in the stock market, so he'll feed you BS to get your money one way or another.
2. If you end up discovering a good trading strategy and share with your mentor, he'll steal from you, discourage you to trade it or even trade against you...
Sorry to say, but there are no short cuts and you'll have to put the work to reap the benefits... There are no friends in the stock market..
where to get real-time data?
what api allows you to trade stocks?
https://www.alphavantage.co/documentation/
https://iextrading.com/developer/docs/#getting-started
The majority of discount stock brokers provide API, here is one example:
https://www.interactivebrokers.com/en/index.php?f=5041
Historical data, the cheapest I can find 20+ years of data fro less than a $100 was on eBay, just search for: "us historical stock market data"