In the show, Both Jirou Yakuin and Akari Watanabe are described as highschoolers, therefore we assume that both of them should be around 18 years old.
There is no official height data for the main characters yet. By observing Jirou and Akari’s height difference in the Official Bakanime Trailer, we can see that Akari’s maximum height reaches the nose height of Jirou. According to an article from Escape to Asia, adult Japanese males have an average height of 5’7 while females have an average height of 5’2. By using Hikaku Sittater to visualize the difference, we found out that a 5’2 girl, when placed beside a 5’7 man, would indeed be around nose height level to the man. With this calculation, we came up with the conclusion that there should be around 5 inch difference between the height of Jirou and Akari. If any official data about the height is revealed, we can simply scale the characters next to one another to get an approximate height for the characters.