It's really a supply and demand issue. Do you live in a AEA Market that can support you and the lifestyle that you wish to live as an AEA Stage Manager? Remember, although turning AEA can open up higher pay jobs - it also may put you in a larger group of people competing for those jobs. And there is no "early-career" AEA card, once you get your card you are competing with every other SM who has an AEA Card . . . the only thing that might separate those applying for specific jobs is pay level - you won't find a lot of Broadway PSMs applying for AEA Showcase or a low paying SPT contracts, but you never know . . . you might find that AEA contracts you maybe taking may pay less the some non-AEA contracts - but you are going to be winding up for bigger contracts down the line. (For example, at the theatre I work at currently, the hourly PA's make more then about most SPT contracts in town.)
You also have to look at some other the other AEA benefits . . . healthcare, pension, workplace protection, workplace rules . . . etc.
The job of SM and ASM are very different, and you may find you are more suited towards one or the other, which may sway your decision.
Only you will really know if you are ready, willing and able to take your card. Many people have full and exciting theatrical careers without ever turning AEA and some people fast track their career by turning AEA early. Just remember, once you turn AEA, there are very few exceptions in which case you can work non-AEA.