I wouldn't worry either, especially when it involves HGST. These are exceptionally good drives, hence the 5 year warranty. In February 2016 I bought 2 3TB HGST drives, both of them produced also in 2014. They're running non-stop ever since, in a small business server, and are in perfectly good condition SMART wise.
For your peace of mind, have a look at the Blackblaze's stats:
HGST drives have extremely low failure rates, around 1%, some models way bellow 1%. Their price and the 5 year warranty are well justified.