The IIRA (International Indoor Rowing Association) rulebook states that the Lightweight classification is as follows:
Men 165 lbs/75 kgs and under
Women 135 lbs/61.4 kgs and under
*By World RIC rules, Junior event participants (ages 14-18) must have been born on or after Jan. 1, 1992 AND be enrolled in high school (or lower grade) as of race day. No one under age 14 may row in the World RIC.
Prior to 2019 there was a qualification time standard for WIRC. That has now been eliminated but a travel stipend will be issued if you submit a qualifying time