You're overthinking it hun.
If they ask, feel free to disclose it at your own discretion. 23 isn't that old really. And the majority of people will be inquisitive; what did you do before you decided to study again, why have you studied again, etc.
And I think you being older than the 18 year olds is a blessing. Sure, you're not that much older but you may have experienced things many 18 year olds haven't. First relationship, first this, first that. You'd be surprised.
You don't need to randomly tell them you're 23. Life goes on lol.