As a solo traveler, you are obviously challenged by people not knowing you or simply not knowing that it's your birthday. In which case of course nothing happens. If you know people around you, they might organize some small souvenir for you or pay for some drinks/dinner.
I once spent my birthday on a business trip also by myself in Sapporo or Osaka, don't remember, but I do remember going into a bar for some drinks and after starting a conversation with the bar keeper and some other people there, I mentioned it was my birthday. I got some music CD the bar was selling as a gift and someone offered me a drink, so I was quite happy, and had some great talk with the other people that I just met for the first time 1 hour ago.
In general, nothing special happens if people want to be nice to you that is different from what happens in other western countries. Maybe a cake, maybe a drink etc.
Just for reference, the only other special birthdays I know of are 20 and 60, 20 because you will be allowed to drink and smoke (expect lighters and other stuff as gifts) and at your 60th you get to wear red clothes, celebrating this one as a very special day.