It's not about a special date as much as it is about creating milestones. You only get one chance to live 18, only one chance to live 21 and only once chance to live 30. Birthdays are a natural, and personal, [way] of marking the end of one year and welcoming in the next with happiness in one's heart and the company of friends and family.
We, as pagans practicing Wicca with Inner Circle Sanctuary, think differently. Here are some wise words from our beloved High Priest, Lord Tanys.
"Here are some religio-magical reasons to celebrate your birthday the best you can:
1. It is your very own Holy Day.
2. It is when your soul (the real you, eternal and divine) entered your body (vehicle) for this incarnation.
3. It is when your Holy Guardian Angel/Daimon/Augoides/Higher Self attached Him/Herself to you for this go-around.
4. It is your personal New Year's Day.
5. It is the beginning of your Wheel of the Years.
6. It is the beginning of your Solar Year.
For more information on this, read Laurie Cabot's Book of Shadows.
7. In a real sense, it is your First Initiation in this incarnation.
So please observe your own birthday with joy. Try to take the day off. Try to do some magic (ritual, divination and/or meditation, etc.).
You are worth it!
"...the position of each and every galaxy, star, planet and celestial body in the universe that was, will never be the same again. (ever)"
CBS Minnesota has an article on how the birthday celebration is pagan in origin with some other great tidbits of information.
The Inner Circle Sanctuary is a school for traditional style Wicca and holds eight sabbat festivals every year.