My son suddenly began to say "Hey!" when someone came into the house when he was about seven months. He never crawled, but started walking when he was barely nine months, and kept running pretty much constantly from then on. My daughter started crawling at about 5 1/2 months, so she took a little longer to walk. About 11 months. Her first word was later than her brother as well - around eight months. But the odd thing is that even though he hit many milestones earlier than he did, she learns academic type things far faster than he does.