There are a number of factors to decide when answering this question.
For example;
What limits are you playing?
How many hands are you playing per day, week, month or year?
What games are you playing?
How good is your bankroll management?
The simple answer is; IMO until you play 100,000 hands+ at the same limits and at the same game, you shouldn;t be in a positon to comment.
I have friends that are really good players. Yet they will never be pro's because they although they read the game really well, they have no concept of bankroll management. Their play would suggest they're good, yet long term, they never have anything to show for it.
I think (and I could be wrong), but i read an article to suggest that 95% of online poker players are losing ones.
First 6 month I played I lost every deposit I made.
Then I managed to hold my own and slowly build a BR, but never considered my self a winning player for the next 9 month.
Then I had a huge rush at tournaments and made some real money in poker for the first time ever (funny enough, that month was my dead line to fit or fold)
That was last october!
Since then I did climb up through the levels, but still didn't consider my self a winning player... am guessing that if I stuck with one level I would have killed it much quicker, but since my BR was big enough to the higher levels I decided to climb as soon as I felt somewhat cofortable.
Now (after almost 2 and a half years playing poker) I'm ready to start considering that I might be able to do this for a living (been doing this full time since last July)...
The journey is long for most of us but if you stick to it and take it seriously you should be able to do it.
The defintion of "winning player" can be very loose.
Daniel Negreanu once wrote some semi-famous article about 2 different types of players.
Player A would consistently play the same limits day after day, grinding it out and slowly but surely accumulating money. He'd never move up in limits, because he found a beatable game, yet he wouldn't play in maybe higher limit games because they were "unbeatable" to him. Is this player a "winning player (can easily grind softer games)", or a "losing player (can never take a shot since he know's his style would get torn up in higher games)"?
Player B, was much more aggressive, with say, game selection, hand selection, more unorthodox playing style, etc. He'd win a Ferrari, lose a Ferrari (cue Brad Booth, lol) in a session or 2, but occasionally make huge scores that player A would be incapable of. Brian Townsend comes to mind. He ran like god for about a year, then had a huge downswing. Does that make him more of a winner than Player A (had much bigger wins), or more of a losing player (losing his roll at a table and maybe getting staked by someone to play in his next tourney) than Player A?
It's all relative. Sample size means something I guess, but it still comes down to what you consider to be a winning player. If you want to consistently win at happy meal stakes online, it can be done in a relatively short amount of time. But if you're not content winning $4 per session and wanna be a winning player against Doyle & Antonius playing on HSP, then good luck, you have lots of work to do.
There is a way to exclude the possibility of being losing player. If you start with freerolls and use those few bucks to build the bankroll, you have nothing to lose, you can only win. If you lose it all, just start over again. It's good, if those few bucks mean much to you, so you don't play recklessly. If you just deposit 50$, which means nothing to you, it's much more probable you bust soon. I had to start twice, then I kept it up...