A puppy that young is rare in a rescue. Are you certain this is a reputable rescue? Some BYB'rs and brokers often pose as rescues as a way of moving their "stock" more quickly. What's the name of the rescue?
If you're comfortable that it is a good rescue group, then no, I don't think it's too early to bring another home. My Becca was only 6 months younger than Alexander and they were inseparable for more than 11 years and were both extremely bonded to me.
You need to think about whether you have the time and the money to have 2 dogs right now - they take a lot of both.
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He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion. -- Author Unknown