Maggie gave a lot of great comments, and yes, it's a personal decision for every single person of when to turn Equity (if ever).
I want to point out the recent Stage Manager Survey results (available at
http://www.smsurvey.info/). One question asked of those who were Equity was what age they turned union. While 52% joined between ages 21 and 25, there were answers from all ages. One of the more interesting quotes to me in the entire survey was, "Most current AEA members joined in their twenties, though six members joined in their fifties and another joined in their sixties (1%)." So no, it's not too late, if that's your path.
Also, while there is the EMC route to get your card, which is what it sounds like your friend was suggesting, there is also what I call the "Poof, You're Equity" contract. If you've got good experience and seem to have everything it takes for the job, any Equity company can simply choose to give you an Equity contract. I don't necessarily recommend this route (or to think that it's an easy way to do it). I find that companies that do so are often hoping they get stage managers who don't really pay that close attention to the rules...this is technially how I got my card, though I was over 40 points into the system by that point. I had also been around enough that I looked at the rules and realized they weren't doing things quite kosher once rehearsals got going.
EDIT/ADD: Also, some people aren't aware what they're getting into with the EMC program. I'm glad they upped the registration from $100 to $200 so people think a little bit more about it. You get 1 week for every qualified week you work (not all Equity theatres offer it - check the list at
http://www.actorsequity.org/docs/emc/emc_theatres.pdf). With the new system, you're eligible for Equity after just 25 weeks. For an ASM, that's generally somewhere between 4-7 shows. If you're working a 9-month season at a LORT theatre, that's one season, likely. After 50 weeks (usually there's a grace period to finish whatever show you're on, but check), you CANNOT work at an Equity theatre again without being on an Equity contract. You can continue to do non-union work for up to 5 years, but not another chance to shadow an Equity SM. These days, I might suggest that people do at least a show or two before joining the EMC program, and get more experience. But that's simply my opinion, and likely others will disagree.
Take a good look at Maggie's questions and also where you stand financially and what you can logistically do in your given circumstance, to help make your decision.
Best of luck,
Erin