WhatsApp Messenger not showing "last seen" for a contact I have a person in my contact list who is using WhatsApp. He is the only person who's "last time seen" status doesn't show.

I thought he had blocked me but when we texted each other I have realized he didn't.

Also when he's online I can see that he is as well as his profile picture but his "last seen" status remains hidden. What could it be?
There's a relatively new privacy feature on WhatsApp that can disable a person's last seen. When disabled you can see when the person is online but can't see when they were online last. For the person enabling this setting, it blocks others' last seen automatically as well.

You can read here for more information on privacy settings:
https://www.whatsapp.com/faq/en/android/23225461