TABLE 2— Percentages of Vitamin C Deficiency (<11 µmol/L), Depletion (11–28 µmol/L), and Normal Serum Values Among US Males and Females.  So, for example, 17% of males between 25 and 44 years of age are deficient in C ...
(Figure from Hampl)

Serum Vitamin C Value Gender and Age, y <11 µmol/L, % 11–28 µmol/L, % >28 µmol/L, % Male     12–17 (n = 975) 6 17 77     18–24 (n = 1011) 13 22 65     25–44 (n = 2649) 17 23 60     45–64 (n = 1765) 17 20 63     65–74 (n = 955) 11 15 74     Overall 14 20 66 Female     12–17 (n = 1133) 5 15 80     18–24 (n = 1186) 11 19 70     25–44 (n = 3212) 12 20 68     45–64 (n = 1916) 10 15 75     65–74 (n = 967) 6 13 81     Overall 10 17 73