see link.. one of them suggests up to 80 years ..

https://www.google.com/search?q=Thuja+occidentalis+%22Smaragd%22&ie=utf-8&oe=utf-8#q=Thuja+occidentalis+life+span

i suspect these might be older .. lol

https://www.google.com/search?q=Thuja+occidentalis+forest&biw=928&bih=744&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiKw4rKwJTQAhUMzoMKHdBVD-EQ_AUIBigB&dpr=0.9

cultivars shouldnt differ from the species ... except for the part where we move them from their native ranges.. and hope for the best ... none of those pix look like NJ to me.. lol ...

i will tell you.. up here in snow country ... breakage of multi leader plants is the greatest killer of these plants ... as otherwise.. in MI ... there isnt much that affects them drastically .. though of course there is always a potential plague that might roll along ...

i really dont think you are going to find a specific answer to your question ... but it could be fun talking about it ...

arent you on a farm .. if so ... i am wondering.. if you have the space.. for a more aggressive thuja.. like GG ...

ken

Well definitely if this emerald green dies, I will be replacing it with green giants since that would be more money saving because their spread is wide thus less plants to buy and plant.

When you use 'Green Giant' you have to have room for a large tree (unless a sheared hedge or specimen is the plan) whereas 'Smaragd' produces a small tree.

There
is a difference between biological and ornamental life spans, the former is
measured in centuries and the latter in decades. Similar to humans, you look
your best up to 25 or so, but you live much longer than that :-)