UK resident - nearly of legal age, wondering if I can still buy Salvia/Salvia Divornum as it's sold as incense, despite my technically being a minor?

I live within day-travelling distance of Liverpool here in the UK where there are plenty of head shops that will no doubt be selling Salvia/Salvia Divornum as incense, as it's completely legal here. All I'm wondering is, as a short-ass late adolescent who is unlikely to pass as over the legal age, could I legally purchase S/SD from said head shop?

Thanks for any information.