Wharton not as much -- they like them young, but as long as you're under 30 at matriculation, it shouldn't be an issue (although they could be going younger as time goes by, since they have been getting gradually younger - from one of the oldest classes to somewhere in the middle now from what I've heard).
HBS and Stanford are likely going to be stretches or long shots. Their bread and butter are folks with strong blue chip backgrounds within a pretty narrow age range. Yes, there's outliers and those with unusual stories (homeless single mother who starts her own biz), but for the most part it's pretty narrow.
You never mentioned where you went to school, which firm you work at or your overall career other than in vague generalities. As such, it's hard to say. However, if you didn't go to an Ivy/equivalent and your current boutique firm isn't exclusive (KKR, Blackstone, TPG, Lazard, Evercore, blah blah blah), then you're likely a stretch as it is even if you were 25. So to add age on top of that, it could be too many strikes (i.e. there's plenty other folks they would likely take over you - not that there's anything "wrong" with you, but because there's enough other people out there that fit a very specific profile that they covet).