User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170506225314/@comment-29963364-20170507222223

Wait, does Slash Dog story actually take place 4 years before the start of the DxD series?

That could actually give us an exact age for Vali. He would be 16 or 17 at the start of the series, and since 1 year has gone by since then, he would now be 17 or 18.