Hi jtg,
Upto to about the point the Insight volumes replaced the Aid book, Jehovah's Witnesses held that each creative day was 7000 years in length. Thus while they didn't believe the earth and animals where created just over 6000 years ago, it was still within the range of young-earth (6 x 7000 = 42,000). Modern Witnesses now allow for each creative day to be an unspecified length of time and even for one day to overlap with another. Thus an age of 13.7 billion for the Universe and 4.5 billion for the Earth would not be a point of objection. Despite this, authors of Awake! and The Watchtower do not often reference the 4.5 and 13.7 billion numbers.
Nonetheless, Jehovah's Witnesses teach the first human (Adam) to ever have existed was created in 4026 BCE and the first female (Eve) shortly afterwards. They are thus compelled to believe all variation in mitochondrial DNA sequences[1], that passes only through mother to offspring, has happened in the past 6,039 years. Furthermore Jehovah's Witnesses believe all air breathing life, was reduced to what could fit on Noah's Ark and this event happened in 2370 BCE or 4,383 years ago.
Jehovah's Witnesses are absolutely creationists, but are simply less consistent than young earth creationists. They allow chimpanzee to have existed for millions of years, but demand special pleading in the case of a closely related species -- humans.
Cheers,
-Randy
[1] mtDNA sequences can therefore change only via mutation. DNA sequeces provided by male sperm do not impact mtDNA sequences transmitted from one generation to the next.