http://en.wikipedia.org/wiki/Sakura_Kasugano
http://en.wikipedia.org/wiki/Ryu_%28Street_Fighter%29
Given the info supplied by the above sources and my own knowlege on the street Fighter Story, This is what I came up with.
Street Fighter Alpha series takes place before and During the first Street Fighter (in the case of 1 and 2) and after Street Fighter but before street Fighter 2. Now Street Fighter Was released in 1987 meaning that Street Fighter Alpha 1&2 took place during 1986-1987 (please note that SFA 1&2 take place during the same time period as Street Fighter Alpha 2 was just Street Fighter Alpha with more characters and better moves. Plus it fit into the story better with the better endings that explained more. Ok, good.) While Street Fighter Alpha 3 took place in between 1988-1990. Sakura being 16 during SFA 3 would have to be born between 1972-1974. Ryu was born in 1964 (according to my sources, altough some may argue that Ryu is Seventeen in Street Fighter 2, that cannot be according to His Bio thats in the game) So that would make Ryu 8 or 10 years older than her. So, it would all depend on when the story takes place.