She was 17 in Witch on the Holy Night which takes place in 1989. In the original Tsukihime she met Shiki for the first time in 1995 since the story proper starts in 2003. So Aoko was about 23 at the time of their first meeting. But the remake takes place in 2014, So now they meet for the first time in 2006. Meaning Aoko would now be 34 at the time of their first meeting...