I got a brochure on JHU SAIS before I applied. Says here the following:
SAIS at a Glance
School founded: 1943
Number of students: Washington: 675
Bologna: 200
Nanjing: 180
Students by M.A. Concentration:
International policy areas: 66%
Regions of the world: 34%
Academic partnerships: 40 students
Student Body: Male 50%, Female 50%
Number of countries: 70
US Students: 59%
Non-US Students:41%
There's a bit more info but mostly about GRE, GMAT, and TOEFL scores.
Also says that the average age of MA students is 26 with an average work experience of 2.2 years.
Hope this helps.