If you are basing it on work experience, outside of HBS and Stanford, you have to look at Cornell and Tepper as the other schools who seems to have a lot of young folks. Wharton is the clear cut older applicant friendly school, then probably Haas, Tuck, and Yale. Kellogg, MIT, Columbia, Booth, and a lot of others average 5 years with almost the same 80% split. Duke, Darden, UCLA, and Ross have similar means but greater 80% spreads.
HBS: Mean Age 28, Mean WE 42
Stanford: Median WE 47, Mean WE 47, 80% range 27-72
Kellogg: Median age 27, Mean Age 28, Median WE 60, Mean WE 61, 80% range 36-85
Wharton: Median age 28, Mean Age 28, Median WE 70, Mean WE 70, 80% range 48-96
MIT: Median age 28, Mean Age 28, Median WE 60, Mean WE 57
Booth: Median age 28, Mean Age 28, Median WE 59, Mean WE 60, 80% range 36-86
Haas: Median age 28, Mean Age 29, Median WE 60, Mean WE 66, 80% range 40-97
Tuck: Median age 29, Mean Age 29, Median WE 61, Mean WE 67, 80% range 37-105
Columbia: Median age 28, Mean Age 28, Median WE 54, Mean WE 58, 80% range 32-87
Yale: Median age 27, Mean Age 28, Mean WE 64
NYU: Median age 27, Mean Age 27, Median WE 56, Mean WE 59, 80% range 36-86
Duke: Median age 28, Mean Age 29, Median WE 60, Mean WE 65, 80% range 36-100
Ross: Median age 28, Mean Age 29, Median WE 57, Mean WE 63, 80% range 36-101
UCLA: Median age 28, Mean Age 28, Median WE 60, Mean WE 61, 80% range 36-96
Tepper: Median age 27, Mean Age 28, Median WE 48, Mean WE 58, 80% range 12-120
Darden: Median age 28, Mean Age 28, Median WE 48, Mean WE 52, 80% range 24-84
Cornell: Median age 26, Mean Age 27, Median WE 60, Mean WE 56, 80% range 36-84
HOWEVER, I would suggest thinking about the employment part of the MBA. Getting a job outside of MC/IB is tougher when you have less than 4 years work experience, and MUCH tougher when you have less than 3 years. Lots of companies wont even interview people with less than 3 or 4...heck there are some who require 5 or 6 years as a minimum. HBS is young since they have been placing so many people in finance (IB, IM, HF, VC, PE, etc.) for the last few years and they feel that medical and law school are their real competition, and those tend to attract young applicants. I think 4-6 years is the sweet spot for experience for most people, since you really have little responsibility to talk about prior to that.
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Kellogg Class of 2010...still active and willing to help. However, I do not do profile reviews, don't offer predictions on chances and am far to busy to review essays, so save the energy of writing me a PM seeking help for these. If I don't respond to a PM that is not one of the previously mentioned trash can destined messages, please don't take it personally I get so many messages I have a hard to responding to most. The more interesting, compelling, or humorous you message the more likely I am to respond.