Sharada Act fixed the minimum age of marriage of girls and boys respectively as

The Child Marriage Restraint Act, 1929 — widely known as the Sharda Act after Rai Sahib Harbilas Sarda, who piloted the bill in the Central Legislative Assembly — was British India's first law to fix statutory minimum ages for marriage. Rather than banning child marriage outright, it defined a "child" by sex-specific age thresholds and made marrying a person below those thresholds a punishable offence.

As enacted in 1929, the Act fixed the minimum marriageable age at 14 years for girls and 18 years for boys. Any marriage solemnised below these ages attracted penal liability under the Act. This is exactly the pairing given in the question: 14 years for girls and 18 years for boys.

Checking the other pairings against the Act's own text:

• 15 and 21 does not match the ages fixed by the original 1929 Act, whose text specifies 14 and 18, not 15 and 21.

• 16 and 22 likewise is not the pairing written into the 1929 Act.

• 12 and 16 also does not correspond to the ages the Act specifies.

Hence, the Sharada Act fixed the minimum marriage age at 14 years for girls and 18 years for boys — the pairing "14 and 18".