I have not yet come across an example of anyone under six being baptised, but I have found a couple examples of seven year olds, and another six year old. I have also come across scores of examples of 8 and 9 year old children being baptised, and literally hundreds of examples of 10-15 year olds.
“In 1934, Mom and Dad were baptized. I too wanted to get baptized, and I kept insisting until Mother asked an older Witness to talk with me about it. He asked many questions in a manner that I could understand. Then he told my parents that I should not be prevented from being baptized; it might harm my spiritual growth. So I was baptized the following summer, when I was still six. (WT Aug 1, 1996, p21)”
“Reared in such a spiritually rich environment, I made my dedication to God and was baptized before my eighth birthday. (WT Oct 1, 2000, p28)”
“In September 1938, my parents were baptized. My siblings and I were baptized in December 1941 at a national convention held at Hargreave Park in Sydney, New South Wales. I was seven years old. (WT Oct 1 2006, p12)”
I particularly like the reasoning of the “elder” in the six year old’s case – “it might harm her spiritual development if you don’t allow her to get baptised”. It would be funny if it wasn't so tragic. And while this happened nearly a century ago, it is quoted here with approval in 1996, showing that they would do the same again today if the occasion arose. Indeed they have done so, as shown in R&R’s example earlier in this thread.
The Watchtower makes a lot of noise about the unscriptural and illogical practice of infant baptism, but they clearly ignore the concept of “age of consent” in this matter. It shows something of their ingrained hypocrisy, when they can say the following, while continuing to baptise children, I mean, who on earth would consider a six year old to be anything other than a "small child"?:
“Jesus’ words at Matthew 28:19, 20 show that it is those who have been made his disciples that should be baptized. Hence, it follows that no infant or small child could meet the Scriptural requirements for baptism.” (WT March 15 1988, p14)”