I bought a boat used and it had a Navionics Hot Maps Premium south version 6 chip with it. Based on this can I tell the age of the chip and if there is a newer version?

Since mid 2010 when Navionics started the Freshest Data Update program and discontinued the annual issues, all the cards are version 6.
It is up to the purchaser to keep up with updates. There are about 2000 updates done every day "somewhere".
If the previous owner did any updates, the age of the data is that day. If the owner did not do any updates, the data can be as old as mid 2010.
A new purchase includes a year of Freshest Data Updates with no restrictions for how many times the updates can be done.

A Premium card subscription cannot be renewed, but can the replaced with a Navionics Update card that can be renewed after than year has expired. That card is $99 as compared to the Premium card at $149.
The Navionics Update card is activated by the expired Premium card so it becomes the 2GB version of Navionics+ with no maps.
Navionics+ is not regional so you can download any location in the US and Canada including waters that the Gold edition has, plus you can download the Sonar Charts map layer.
Once the activation has been done, the Premium card is locked so it cannot be used again to activate another Update card, but you do not loose the use of it.

The current Navionics+ Preloaded has all the maps for the US and Canada, plus the Gold coverage, and is a 16 GB card. It can be loaded with the Sonar Charts map layer too.

One more thing, the current maps can be viewed on the Navionics website's Web App so you can compare what you have to the current data.
The Web App is updated daily and has both the Navionics maps (Nautical Charts) and Sonar Charts map layers.

For older cards for the South region:

S5 is 2009
S4 is 2008
S3 is 2007
S2 is 2006
S is 2005