Speaking from an honest viewpoint, most of the people interested in this blog have played Dnd for 5+ years at the least. I, in all of my 17 years of worldly experience broke into the game about three years ago. In this time I have played under six different DMs and run about four campaigns myself. As you can see I'm a bit behind the experience bandwagon.
Having played (and currently playing) in games with older DM's who have been involved for 20+ years has definitely given me the ability to reflect upon the weaknesses and strengths of my own DM'ing style.
Under both of these Dungeon Masters the games have been absolutely enthralling, capturing my imagination and sending the PC's home with electric excitement making the next session seem too far away...
The DM of the campaign I am currently PC'ing in is actually one of my own player's father, therefore I have dual aspects of reflection from myself and my PC.
There is an undeniable art to DM'ing, there are aspects that must be learned. How to appeal to player's, the balance between established rules and imagination, and how to read the PC's to know just what to put in a game. Not to mention the skill of world-building and story telling. So for now I'm doing my best to observe these skills in action from more experienced DM's in hopes of making my games better.
One of the thing that frightens most people about being a DM is how much you have to know. On the one hand this is a misconception, you do not need to know everything in the rule books. On the other though...you have to have knowledge of the fantasy genre. I was able to come into the game so easily because the sheer fascination for the fantastical I had possessed all my life. Being older allows for a greater scope of that information, and a vast pool to draw from when creating stories.
Being a Dungeon Master is like being an actor, you never stop learning. No matter how many years you've played I think there is some aspect that will need perfecting.