It is not clear to me whether you are talking about someone older or younger than you. That's going to depend on your age and that person's age, because if you're 30 years old, you can date someone 10 years younger, but if you're 20 years old, you can't. Nowadays society is more and more tolerant of such things, so I wouldn't worry too much, the only thing is that the greater the age difference, the more difficult it is for the relationship to work, but it's always worth a try.