How can I convert this column into a whole number instead of a decimal?

How can I convert this column into a whole number instead of a decimal?

After setting the DataSource for your DataGridView, specify the numeric format of that column:
dataGridView1.Columns["age"].DefaultCellStyle.Format = "N0";
Well, I'm not sure exactly where your code is, but in general you'd say
Convert.ToInt32(age)