Not too long ago, there was a post here about how Shenhua could be a ghost/reincarnation. After looking closely at the cutscene which explains the Shenmue tree, there is no doubt in my mind that this theory is at least partially correct. There is a dramatic contrast in the size of the tree when comparing Ryo's encounter with the flashback of when Shenhua was an infant.
The second image isn't great, but you can still clearly see the difference in size.
Shenhua explains to Ryo (if you prompt her) that the Shenmue tree is thousands of years old, and "... was already that tall when my (her) grandfather was a child."
This either means that the tree pictured in Shenhua's flashback is a different Shenmue, or Shenhua is much older than sixteen. The former is unlikely since Shenhua's father refers to the tree her cradle is hanging from as "The Shenmue," not "a Shenmue." I know it's not completely solid, and there could be some variance caused by the translation, but it seems to me like they were specifically talking about this one Shenmue tree, the same one seen by Ryo.
Another clue is the buildings seen behind the Shenmue tree. The ones seen in the flashback are vastly different from Shenhua's house, which Ryo enters. This means either a different location, or a difference in time which could be any amount.
A possible contradiction is Shenhua's explanation of her father. He adopted her, and is not the same man seen in the flashback. It is very possible that his house is not on the same land that Shenhua's real parents lived on, and he just happened to also have a Shenmue tree in front of his house. However, there is no evidence that Shenhua's adopting father even lived in the same time period as Ryo. He is never seen in Shenmue II, and leaves a mysterious note in a cave before disappearing.
Am I just trying to make something out of nothing? Or is Shenhua hundreds or thousands of years old?