Those searching for the Fountain of Youth may find age-defying rejuvenation in two facials soon to be offered at the more than 16,000-square-foot spa at the Mandarin Oriental, Boston—a Robb Report Top 100 Hotel. On October 1, the spa will add to its treatment menu the skin-care line of Linda Meredith—renowned as the “Queen of Facials,” thanks to her 40-plus years’ tenure in the beauty industry. The Spa at Mandarin Oriental, Boston, will offer two of her signature facials, the Couture Facial and the Couture Fac…