So Sonic is nearly 17 by frontiers right?

I know Sonics age is not a cut and dry thing but time clearly passes so he is aging, whether sega likes it or not.

In forces, Sonic is "tortured" for 6 months. Episode shadow takes place one month before, with a cutscene showing shadow meeting infinite a fee "months" before that. So at least 2 months, plus 1 plus 6, so 9 months.

Sonic is 3 months away from being 17 assuming forces takes place in the same month of his birthday.