Hi,
I'll defer to the Aikido practitioners here, but I believe that Aikido (in most schools/organisations) have two belts: white, and black. There is a kyu-grade structure for the white ranks, I have seen different schools range from 3 kyu grades, to 6, to 9 depending on the instructor(s) and the school. Yudansha (black belt graded students) also wear hakama.
The time taken between grades depends again on the instructor, the organisation/school, and obviously the student, but the idea of 5 years plus to achieve Shodan would be average from Aikidoka I have spoken with.