3.

The average weight of a healthy brain in pounds. The actual weight of the brain varies between males and females, with males having the heavier brain. Just so you know, the weight has no effect on determining your intelligence level. (Source)

73.

The approximate percentage of your brain that consists of water. Only a 2% dehydration level can negatively affect your performance in tasks requiring attention and short-term memory. In addition, your brain consists of nearly 60% fat, making it the fattest organ in your body. (Source, Source 2)

85 billion.

The lowest estimate of the number of neurons in the human brain. Estimates range from 85 billion to over 120 billion but no one has been able to accurately determine the exact number just yet. (Source)

150.

Milliseconds needed for a thought to be generated and acted upon. The definition of a thought here is a reaction to a sensory trigger. If your team scores a goal, you basically need at least 150 milliseconds to start reacting to it. In other words, almost half the time of the blink of an eye. In general, some estimates say that the brain processes thoughts at 260 miles per hour. Faster than the fastest F1 car available. (Source)

No limit

Numbers of years to pass before your brain can no longer learn. Our brains are able to learn new things every single day of our lives. There is literally no limit to our learning. (Source)

As we grow older, our mental capacities might decrease but that does not mean that our brains are unable to learn. Active aging brings some negative elements to it such as decreased awareness and focus. On the other hand, our experience is as high as it will ever be.