Can the frontal lobe shrink by any means? will it grow back?

Yes: As we get older, the cells, tissues and organs in our body shrink/atrophy, degenerate/decrease in its functional capacity and it's part of the natural cycle of the human body. When the brain shrinks, it doesn't grow back. Those people who are endowed with good genes have a longer life span and have a delay in these processes. Google online for images of brain atrophy. Best wishes!