Can I postpone the gain on the sale of my home if I buy another house?

No- That was an old rule than has not existed since the 1980s. Currently, if you are single and live in your home for 2 out of the last 5 years, you can exclude up to $250,000 of the gain. A married couple filing jointly can exclude up to $500,000 of the gain. Any gains that exceed these amounts would be taxed at the capital gains rate.