How do Hindus celebrate birthdays generally?
I think this is an opinion-based question. Most Hindu families living in urban areas these days have lost track of their roots and tradition on how to celebrate birthdays. They now simply resort to imitating the West by lighting candles on a birthday cake and blowing out candles.
The more pertinent question is:
How should a Hindu celebrate the birthday?
First off, it is very important to celebrate ones birthday - should not neglect it. One should celebrate the birthday on the tithi they were born rather than a specific date from the English calendar. (You can calculate your Janmatithi from here).
Wake up very early in the morning and start your day with abhyanga-snana i.e. take bath after applying oil, head to toe.
Before you take the bath, have your parents and elders also apply some oil to your head and back (spine). Take their blessings. It's most important to take blessings of your parents and guru on your birthday. The elders in return usually bless by uttering:
Shathamanam bhavathi
shatayuH puruShaH shatendriyaH
aayuShyevendriye pratitiShThati
(a blessing to live for hundred years)
After taking bath, pray to your kula-devata or ishta-devata.
Then take a concoction of cow milk, jaggery and black sesame seeds. Turn to east and swallow the mixture 3 times (achamanam). This should prevent any obstacles you might face now until your next birthday.
Next, remember the names of the 7 chiranjivi's (by birth):
Ashwathama, Mahabali, Vyasa, Hanuman, Vibhishana, Kripacharya and Parashurama. Or simply say out loud:
अश्वत्थामाबलिर्व्यासोहनुमांश्च विभीषण:
कृपश्चपरशुरामश्च सप्तैतेचिरंजीविन:।
Ashwathaama Balirvyaaso Hanumanshcha
Vibhishanah Krupascha Parashuramashcha
Saptaitey Chiranjivinah
Ayushya Suktam from the Yajur Veda can be recited for a long and healthy life. Optionally, Ayushya Homam may also be performed.
Visit the nearest temple
One can eat the most delicious food they like but should maintain brahmacharya the entire day.
If you can afford, donate food and clothes to the needy. If you cannot, feed green grass to a cow and circumambulate (pradakshina) the cow 3 times.
Even by mistake, don't blow out candles or deepa (diya) as "candle-blower" (or it's equivalent in Sanskrit) is a derogatory term used for thieves - the idea is that before robbing a house a thief blows out the light source!
References:
How to celebrate our birthday by Chaganti Koteswara Rao (YouTube video in Telugu)
How to Celebrate Birthday on Bhakthi TV's Dharma Sandehalu (YouTube video in Telugu)
