People of different ages who share the same birthday

You're not going to like this answer, but a mother is someone who always shares the birth days of her children. If she has three children, she has four birthdays, three of which she shares with her children who are always younger than her. I told you you wouldn't like it!

In common usage, a birthday carries one of several slightly different meanings:

• the day a person was born
• the anniversary of the day a person was born
• the celebration on the day a person is born
• the celebration on day of the anniversary of the day a person was born
• the day of a birth

Irish twins

What are Irish twins? Well, long story short, Irish twins are siblings that are born 12 or less months apart.

The strict definition of Irish twins encompases more than what the question specifies, however, it is a close enough answer to list, because Irish twins will not be the same age and could share the same birthday, only a year apart.

Further, though it could be applied to siblings born less than 12 months apart, far and away the most common use of the phrase Irish twins is to describe siblings exactly 12 months apart, but notably it is less commonly applied also to cousins with the same birthday, any relatives with the same birthday, and even close friends with the same birthday.

Birthday twins

I have no citation, but have often heard this used to describe exactly what is asked: two or more, not necessarily related, born on the same day, regardless of year born. Other forms of the same construction are "astro twins," "astrology twins," and "star twins."

connascent (kəˈneɪsənt) Definitions adjective born, produced, or growing simultaneously

I wonder if it can be used here ??...

I imagine that any word for this would seem boring as a non-starter. To try to brighten things up a bit, from some other source, how about calling such persons products of the birthday paradox, which is an easy observation about persons with the same birthday.

Have you ever noticed how sometimes what seems logical turns out to be proved false with a little math? For instance, how many people do you think it would take to survey, on average, to find two people who share the same birthday? Due to probability, sometimes an event is more likely to occur than we believe it to. In this case, if you survey a random group of just 23 people there is actually about a 50–50 chance that two of them will have the same birthday. This is known as the birthday paradox. Don't believe it's true? You can test it and see mathematical probability in action!

[Scientific American]

For good reason, as is often the case on forums such as this, I rarely post the bulk of what "comes" to me. Let the down voting begin. As a murderer might say, maybe, I can get me a score of -7, that is if this one stays up long enough.