21st Century Conservation Corps Act This bill provides funding for FY2021 to the Department of Agriculture, the Department of the Interior, the Department of Homeland Security, the Department of Labor, and the Department of Commerce primarily for federal land management and other conservation purposes. The funding provided by this bill is designated as emergency spending, which is exempt from discretionary spending limits. The bill also establishes the Outfitters and Guides Relief Fund; expands the Every Kid Outdoors Program to include fifth and sixth grade students and home-schooled learners 11 and 12 years of age, who shall be provided free access to federal lands and waters under the program; establishes the Forest Service Legacy Roads and Trails Remediation Program; establishes the 21st Century Civilian Conservation Corps program to support youth and workforce development programs; provides for the temporary waiver of ski area permit and rental fees; provides for the temporary waiver of outdoor recreation land use permit fees; provides for the use of the Reforestation Trust Fund for the reforestation of certain National Forest System lands, Bureau of Land Management lands, and Bureau of Indian Affairs lands; establishes the Reforest America Grant Program; and extends through FY2030 and revises the Conservation Stewardship Program, including to provide additional funding for conservation activities related to climate stewardship practices.