Its going to be somewhere between 50-58 for me. 50 is the earliest i'm eligible for early retirement in the federal system, 58 is my full retirement eligiblity. I just wouldnt want to earlier than this anyway, because I believe the real power of compouned growth simply needs time to do its magic, and there's no way around it. Because of this and because of IRA contribution limits, it can be statistically shown you have to work exponentially harder (meaning save exponentially more) to shave more and more years off of retirement. At some point, I believe the tradeoff (of breaking your neck to get into the lower 40s and 30s) becomes not worth it.*
* Also, I define my ER point, the point at which my wife and I could both completely get by without either of us working. If my knew for certain my wife would work and i wanted to rely on that, then i'm just "not the breadwinner", not really an ER. Now she may just want to work to give her something to do or to get away from me, hee. But I personally wouldnt quit until that was just an option for her, not a necessity.
I grew up in a family where my mother never worked. For her to have claimed she was an ER (cause she taught school one year) would have been a silly, and misleading claim.