for example, the first parameter rule, passed in checkage does not seem to be used in the body of this function, so ask for advice.
  <el-form-item label="" prop="age">
    <el-input v-model.number="ruleForm2.age"></el-input>
  </el-form-item>   
    export default {
    data() {
      var checkAge = (rule, value, callback) => {
        if (!value) {
          return callback(new Error(""));
        }
        setTimeout(() => {
          if (!Number.isInteger(value)) {
            callback(new Error(""));
          } else {
            if (value < 18) {
              callback(new Error("18"));
            } else {
              callback();
            }
          }
        }, 1000);
      };
      return {
        ruleForm2: {
          age: ""
        },
        rules2: {
          age: [
            { validator: checkAge, trigger: "blur" }
          ]
        }
      };
    },
    methods: {
      submitForm(formName) {
        this.$refs[formName].validate((valid) => {
          if (valid) {
            alert("submit!");
          } else {
            console.log("error submit!!");
            return false;
          }
        });
      },
      resetForm(formName) {
        this.$refs[formName].resetFields();
      }
    }
  }