Impossible question to answer. But you're making an easy mistake to make. Trading and making money from trading for 95% of the winners is not like a normal job. In a normal job you go to work everyday, do what you're paid to do and then get pretty much the same paycheck every month.
In trading if you're going to make say £12,000 in a year then this could be broken down into £1000 a month in winnings. But in reality you may well lose money for the first 3 months, breakeven for the next 2, have a great run for 4 months (making £12,000) and then breakeven for the remainder of the year, hence making £12k.
As for listening what other people are making then my advice is to believe NO ONE in this business when it comes to money. 90% of the losers will tell you they're making or breaking even and most of the clever winners will tell you the same. The ones that tell you they're making a fortune, well they're the ones I'd trust the least.
So how much can you make, depends on how good you are OVER a period of time. Your guess on this fact is as good as mine but your friend hints on the truth that most people lose or at least break even over time. My advice for most people is to treat this game as a hobby to start with (say 1-2 years), play with small money, money that it doesn't matter if you lose. Then if you really can make it in the business you'll know about it within this timeperiod, in effect you can't kid yourself of your own abilities or lack of them.
Good luck anyways