I'm tempted to comment on some of the responses but as it appears you're either trolling the OP or you just really have no clue what you're talking about.
First off, danoscar...
You need to focus on ONE discipline (whether that be cash games , sng, or MTT). I'm guessing this would be difficult in SNG's these days as there's not many sites offering many games (
partypoker it's achievable at micro/low stakes but you'd need to play an IMMENSE volume... far more than I think you can imagine).
Once you've chosen which discipline, you'll need to study and put in some volume.. then study some more.. put in more volume etc.
The thing is, you'd already KNOW if you're able to win $500/mth. income from
online poker prior to trying because a) you've managed to do this already or b) your winrate over a decent sample size, playing a game you know you can beat shows that it is more than possible for you (but also keep in mind if you're able to put that amount of TIME into it 'and' that you have a good mental game and are able to deal with variance)
My suggestion without even knowing what games you have experience in would be to play MTT's, start out at $1 to $3 buyins, play them til' you feel comfortable beating them. You'll find a larger % of bad players in micro/low stakes MTT's vs. cash games.
Study, play, study, play.
THen play some more! lol
You really want to be able to multi-table (8 tables minimum should be your target).
To win $500/mth. and assuming you have lots of time on your
hands (you're retired right? ... me too fwiw), you can achieve this by playing an avg. buyin of $5 as long as you're making sure to get into as many MTT's as possible that are smaller field tourneys (not ones with 5,000 entrants in them... although I'd play those as well if you're able to play many tables).
For those suggesting you'd need to play at higher buyins to profit $500/mth. is just not true.
And if cash game is your choice to play, you'll get CRUSHED at 50nl games so that suggestion is a really bad one imo. IF you're wanting to play cashgame you'll need to start off near the lowest (or theee lowest) stakes and put in TONS of hands, tons of studying and LOADS of volume! I'd suggest this is a slower way to get to earning $500/mth.
OP,
I am contemplating doing something similar in the not so distant future. I've been planning this for awhile though, lol... but life has thrown some curveballs my way (lots of death in the family this past couple years & my partner is very ill).
Once I get going, if I'm able to help you out in some way, just ask.