since 2009 and when you say "my first experience"..I'm still experiencing, but it took quite some time before things start to make sense if that's what you mean. But that's the same as anything, you just learn and adapt from your mistakes before you find something that works for you.
The question you want to ask yourself is how long are you prepared to learn for/and how much are you prepared to lose in the process.
If you want to invest for a long-term approach, rather than a short-term approach, a couple hundred dollars is fine. If you invested in small and micro-cap companies, you could expect to earn around 15% per year which will return higher as you invest in smaller and smaller companies - if you do it through mutual funds or EFTs in the long run.
There is no some precise digits, but for sure it should be 3-digits sum and more than 250-300$. Just to open reasonable position (Not high-risk scalping) I would advice you to make decent deposit to keep even some percent of rational trading.
Demo trade for a few months. When profitable for a few months then get a job and save up £5000 and start at half stakes. I could go on but got bored repeating myself over the years whilst a lot of people stubbornly remain stupid enough to live trade with no experience and eventually face ruin.
As above -trade with money that wont ruin you if you lose it.