PDD Birthday Party | Monday, June 29

The sixth anniversary is significant because it proves you weren't white-knuckling it for bragging rights of reaching the artificially significant five-year mark. You've gone a whole extra year, signifying an intention to continue well beyond.
That's the best I could think of.

Now We Are Six - A.A. Milne
When I was one
I had just begun
When I was two
I was nearly new
When I was three
I was hardly me
When I was four
I was not much more
When I was five
I was just alive
But now I am six,
I'm as clever as clever;
so I think I'll be six now
for ever and ever

To reach five years is a big leap already, much more for six years! What better way to celebrate it than with the people who made your sixth year possible! Of course the booze will make everything perfect. Have fun on your birthday and may you have another six years ahead!

Because it is my 43rd Birthday today, I'll say that the 43rd anniversary is far less significant than the 6th.  When you're 43, you're expected to know everything, and you can no longer rely on the cute factor to get you out of (most) jams.  Not that I don't still try.  Six can still run wild and over-indulge without having to get up for work in the morning.  Also, 43 is such a non-number.  It's not 40, or 45, and they aren't sending you AARP stuff yet--43 is what you do while you are no longer really young, and you're just waiting to get old.  When people ask how old I am, I'm going to say 106, because at least that is interesting, and then maybe they will say something nice like, "Wow, you hardly look a day over 43."

And that was completely lame, but ironic1 beat me to the Milne.

Happy birthday Shelly! You really don't look a day over 43. . .

I guess there's a difference between an anniversary and a birthday, even through we use those words interchangeably when referring to PDD's six years of existance. 

A 6th birthday is indeed more significant than a 43rd, because 6-year-olds are kids and society has determined that being a kid is a special thing.

But in terms of an anniversary, I think they basically get more significant with every year, except that obviously the round-numbered ones are extra important. (50th anniversary is more significant than 51st, but 51st is more significant than 49th.)

The catch is that the early anniversaries carry extra significance because they carry a sort of kid quality. At age 4, a relationship or enterprise is still new. At age 6, it's mature. So a 5th anniversary is more important than a 6th, and a 7th, 8th or 9th are also more important than a 6th.

See what I'm getting at?