Tell age of SSD by using iostat? I did 


  iostat  -Id disk0


on my MacBook Pro (MacOS Sierra) and found the total number of reads/writes done on the SSD. Is it true that this is indicative of the age of the MacBook? Should a new MacBook have very few reads/writes? Mine has a power cycle count of 10 but a very high number of transfers (2050247) at 28.6 KB/t i.e. around 55GB worth of reads and writes. Something seems off here...
No, iostat gets it's information from the OS, not from the hardware.
You could use smartctl - see this answer