Level 19 is about the "middle" of the Aes Sedai strength range (at least for named characters) making roughly 50% of the Aes Sedai being strong enough to Travel.

108 Aes Sedai women above level 19
101 Aes Sedai women below level 19

15-16 years of training seems to be about the average time. 73 women completed training in 16 years or less, 87 women took longer.

Most women spend less time as Accepted than as Novice, in some cases a LOT less time, but most of the time it is no more than 1-2 years longer as a Novice. Team Jordan tended to explain when a woman spend a significant time as a Novice (typically lied about age or was some kind of discipline problem etc).

Weak women generally take longer in training time than strong women. 30 women managed to achieve the Shawl in 10 or fewer years only 4, Amico (27), Lyrelle Arienwin (24), Vandene (22) and Adeleas (23) had weaker than 19 strength.

Of the 73 women who achieved the shawl in fewer than 16 years 24 had less than 19 strength.

of the 87 remaining women with training times, 38 were below strength 19

Black Ajah seems to skew high in strength ... of the 34 Aes Sedai we know are Black and have a strength score, only 8 are weaker than level 19

Nationality breakout (every nation is represented):

52 Andorans (counting Two Rivers)
45 Seanchan
44 Aiel
24 Sea Folk
24 Taraboner
23 Domani
21 Arafellin
18 Tairen
17 Cairhienin
17 Saldaean
16 Murandian
14 Kandori
12 Illianer
9 Altaran
8 Ghealdanin
6 Far Madding (including a False Dragon)
6 Shienaran
5 Amadicians
3 Mayener
2 Black Hills
1 Malkieri (counting Nynaeve as Andoran)
1 Sharan
1 Tinker

Age Ranges

4 400-600+
11 300-400 (2 Aes Sedai lived past 300)
24 200-300
76 100-200
58 50-100
68 <50

Ajah

39 Blue
53 Brown
48 Gray
60 Green
42 Red
37 White
45 Yellow
42 Black

*please note that not all Aes Sedai had complete information on strength, training time or Ajah etc so the numbers here don't add up consistently.