Nobody 25 or over other than Andrew Redmayne and Storm Roux. Only two foreigners (Scotsman Noah McCann, age 37 and Kiwi Storm Roux, age 33). United actually fielded three foreigners (Japanese Koya Nakano and Tomoki Wada, and Fijian Leroy Jennings). Sofascore says that Lucas Mauragis (CCM) got MOTM based on ratings.
Mariners' starting 11 had an average age of 23.2, which seems reasonable but that doesn't account for two things: A. the obvious outliers (they fielded guys aged 33 and 37) and B. the bench (which was all under-19s except for Harry Steele). In comparison, United fielded an 11 with an average age of 25.8 but without extreme outliers (since there was more diversity in the ages of their players, whereas Mariners had a 17-24-year-olds plus a 33-year-old and a 37-year-old).