Prior to his professional career Frostwick played for North Berwick Rugby Club and Currie Chieftains.
[3][4] Frostwick in November 2021 was put on loan to English Championship side Ampthill Rugby Club, to gain valuable game time.
Frostwick started consistently for the Ampthill side until Edinburgh required him back in early February 2022.
In early June 2022, Frostwick moved to Sydney Australia to play for Shute Shield side, Warringah.
It is believed Frostwick returned to the Scottish Capital after the 21/22 Shute Shield season came to an end in early September to join up with Edinburgh Rugby again, whilst turning out for top of the table Super6 side, Watsonians.