Error converting data type varchar to int.

ALTER PROCEDURE [dbo].[gvempdetails]

     @Action VARCHAR (10),
     @EMPLOYEEID Int =0,
     @EMPLOYEENAME VARCHAR(100)= NULL ,
     @DEPARTMENT VARCHAR(100)= NULL ,
     @AGE VARCHAR(30)= NULL,
     @SALARY INT = NULL
     
AS
BEGIN
      SET NOCOUNT ON 
     IF @Action = 'SELECT'
      BEGIN
      SELECT EmpId,EmpName,Dep,Age,Sal
      FROM gvdetails17
       END
       
     IF @Action='INSERT'
       BEGIN
       INSERT INTO gvdetails17(EmpId,EmpName,Dep,Age,Sal) VALUES(@EMPLOYEEID,@EMPLOYEENAME,@DEPARTMENT,@AGE,@SALARY)
        END       
            
     IF @Action ='UPDATE'
      BEGIN
      UPDATE gvdetails17 SET EmpName=@EMPLOYEENAME,Dep=@DEPARTMENT,Age=@AGE,Sal=@SALARY WHERE EmpId=@EMPLOYEEID
      END
      
      
     IF @Action='DELETE'
      BEGIN
      DELETE FROM gvdetails17 where EmpId=@EMPLOYEEID
      END
      SET NOCOUNT OFF
      END

protected void gvDetails_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            if (e.CommandName.Equals("Add"))
            {

                TextBox txtEmpId = (TextBox)gvDetails.FooterRow.FindControl("txtempid");
                TextBox txtEmpName = (TextBox)gvDetails.FooterRow.FindControl("txtempname1");
                TextBox txtEmpDep = (TextBox)gvDetails.FooterRow.FindControl("txtdep1");
                TextBox txtAge = (TextBox)gvDetails.FooterRow.FindControl("txtage1");
                TextBox txtSal = (TextBox)gvDetails.FooterRow.FindControl("txtsal1");

                string Id = (txtEmpId.Text);
                string name = txtEmpName.Text;
                string department = txtEmpName.Text;
                string age = txtEmpDep.Text;
                string salary = txtEmpDep.Text;

                INSERTEmployee(Id, name, department, age, salary);
                gvDetails.EditIndex = -1;
                bind();


            }
        }
        protected void INSERTEmployee(string Id, string name, string department, string age, string salary)
        {

            SqlCommand cmd = new SqlCommand();
            cn.Open();
            cmd.Connection = cn;
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.CommandText = "gvempdetails22";

            cmd.Parameters.Add(new SqlParameter("@Action", SqlDbType.VarChar, 50));
            cmd.Parameters.Add(new SqlParameter("@EMPLOYEEID", SqlDbType.VarChar, 50));
            cmd.Parameters.Add(new SqlParameter("@EMPLOYEENAME", SqlDbType.VarChar, 50));
            cmd.Parameters.Add(new SqlParameter("@DEPARTMENT", SqlDbType.VarChar, 50));
            cmd.Parameters.Add(new SqlParameter("@AGE", SqlDbType.VarChar, 50));
            cmd.Parameters.Add(new SqlParameter("@SALARY", SqlDbType.VarChar, 50));

            cmd.Parameters["@Action"].Value = "INSERT";
            cmd.Parameters["@EMPLOYEEID"].Value = Id;
            cmd.Parameters["@EMPLOYEENAME"].Value = name;
            cmd.Parameters["@DEPARTMENT"].Value = department;
            cmd.Parameters["@AGE"].Value = age;
            cmd.Parameters["@SALARY"].Value = salary;
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
            gvDetails.DataSource = ds;
            gvDetails.DataBind();
            cn.Close();