Hi Firewater, and welcome!
I just read your intro -- I'm solo and dating in NYC too. Of course my experience will be different from yours because I'm a woman and I would guess close to twice your age. BUT generally, I don't use any form of the word "polyamory" when I meet men -- it's just so ripe for misinterpretation (and I don't really like labeling myself anyway). What I usually say is that I'm "not looking for exclusivity right now" simply because the word exclusive seems to ring a bell with people, while polyamory just confuses them -- and I don't feel like educating everyone I go on a date with. I mean, I don't want to spend a whole night out talking about relationship dynamics.
Now, of course on the outset, if I say I don't expect a guy to be monogamous with me, this appeals to lots of men, probably because their first thought is that they're gonna get laid -- and I'm a looker -- but if they've been indoctrinated in the madonna/whore view of women, then they think I'm just slutty and into sleeping around and not relationship material. If the conversation lends itself and I get a good vibe that they're worth explaining myself, I then discuss more about it and how I would like to "cultivate multiple ongoing committed relationships."
Now, I know it is much trickier for a guy to meet women who will be open to this because most chicks have been handed that fairytale wedding to dream about. I don't know what younger gals are into these days but I would hope some are more open-minded. So try using words like non-monogamy and exclusivity rather than polyamory at first and see if they're receptive before you waste your time trying to explain it. I don't know if there's really any right or wrong way regarding
when to tell them (first date or not), I feel that there's nothing harmful in going out a few times before talking about it, because you're still in the "getting to know you" stage, and if it's something they're not really into but they've begun to like you, then there's more of a chance that they might consider being receptive to poly. However, of course, it's important not to lead them on to thinking you're into monogamy until then. Dates should be about enjoying the person and the moment, not auditioning for a role you want them (or yourself) to fit into, anyway, I believe.
Also I've been told that other places where alternative lifestylers hang out are good venues for possibly meeting people open to poly. Look at groups or people involved in or into the arts, gaming, RenFaires, co-housing, BDSM, Burning Man, nudism, sci-fi, Unitarianism, intentional communities, ink and piercings, New Age and other "spiritual" philosophies, etc., where more free-thinking people will be found.
In NYC, I sometimes attend meetings at
OpenLoveNY. Every month they have a poly cocktails get-together (drinking alcohol not required). I know of the meetings you go to (West Side, right?), as some people I know attend as well. There's also the
Pleasure Salon monthly gathering for sex-positive people but be prepared for lots of really kinky types as well as poly peeps.