I don't know if it deserves an entire thread or not but Shueisha shared the data for the demographics of all of their manga magazines which is really interest. Here's the translation:
Shounen/Kodomo and Seinen magazines
Shounen Jump:
Print/Circulation: 1 740 000
Age Groups: 9 and under(3.2%), 10-12 (9.6%), 13-15 (16.4%), 16-18(17.6%), 19-24(25.8%), 25+ (27.4%)
Shounen Jump Website:
880 000 Visitors per Month
2.400.000 pages viewed per Month
Shounen Jump Plus:
2.400.000 Users per week
The numbers of downloads for the apps is 10 million
V-Jump:
Print:187 500
Readers: 90% Male and 10% Female
Division: Elementary school(45%), Middle School(24%), High-school(12%), Workers/Employee(15%)
Saikyo Jump:
Print: 150 000
Divison: Elementary School(86.5%), Middle School(11%), High-School(2.5%)
Jump SQ:
Print/Circulation:210 000(Digital Included)
Age Groups:15-19(25.2%), 20-24(26.4%), 25-29(30.2%),30-34(18.2%)
Jump SQ Rise:
Readers: 91.4% Male and 8.6% Female
Young Jump:
Print/Circulation: 506 000
Age Groups: 20-27(47.8%), 28+(32.3%)
Why do people buy Young Jump?
1.For the Photos of the Gravure Idol inside the magazine 31.4%
2.For the Cover 21.6%
3.For the series they like 12.6%
Ultra Jump:
Print/Circulation: 36 000
Readers:Male(94.8%) and Female(5.2%)
Age Groups: 19 and under(29.4%), 20-24(25.7%), 25-29(23.5%), 30+(21.4%)
Grand Jump:
Print/Circulation: 170 000
Readers:Male(91.5%) and Female(8.5%)
Age Groups: 20 and under(2.0%), 21-30(14.5%), 31-40(14.9%), 41-50(31.7%), 51+(36.9%)
Shoujo and Josei magazines
Ribon
Print/Circulation: 145 000
Division:Elementary School(85.3%), Middle School(11.4%), High School(3.3%)
Cookie:
Print/Circulation: 34 000
Age Groups: 19 and Under(9%), 20-25(18%), 26-30(21%), 31-35(24%), 36+(28%)
Margaret:
Print/Circulation: 38 000
Age Groups: 13 and under(18%), 14-16(31%), 17-19(27%), 20+(24%)
Betsuma:
Print/Circulation: 131 000
Age Groups: 14 and under(12.7%), 15-18(16%), 19-23(15.1%), 24+(56.2%)
The Margaret:
Print/Circulation: 36 000
Age Groups:12 and Under(9.3%), 13-15(29.4%), 16-18(30.5%), 19+(30.8%)
OfficeYOU:
Print/Circulation: 52 000
Age Groups: 30 and Under(7%), 31-34(4%), 35-39(7%), 40-44(11%), 45+(71%)
Cocohana:
Print/Circulation: 54 000
Age Groups: 20 and Under(6%), 20-30(21.6%), 30-40(43.7%), 40-50(25.9%),50+(2.8%)
http://adnavi.shueisha.co.jp/mediaguide/