[Margaret Pilkington]

I also think the early 40's...you have had a chance to gain some life experience......and usually are more comfortable in your own skin (not searching for who you are anymore).....have usually developed the confidence to challenge ideas and values....and are not afraid to speak up for what you believe in.
Most 40 year olds have an abundance of energy......and of course enthusiasm......enthusiasm is what makes others want to emulate you.