What I could find about the pineal gland is that it produces melatonin which in turn regulates sleep.
Though the quality of sleep can have a huge impact on ones life, sleep itself is not that important. If I remember correctly Buddha only slept 4 hours after his enlightenment. I have been told that monks 'suspected to be' arahants also slept only 3 or 4 hours. They don't need more than that. So, the need for sleep will become less and less anyway.
Pineal gland, calcified or not, should not be a hindrance for you to practice the 8-fold path at all. And anyone practicing the path can become enlightened.
Hope this helps.