Is it illegal to date someone 5 years apart?

Yes, its correct that dating is not illegal. Thats because dating is not a specific act. Specific actions that are often associated with dating, like sex, can be illegal.

Is 6 years age gap a lot?

The ideal age-gap for dating is 6 years, where the man is older. The study looked at the price of over 100,000 first dates between older men and younger women. And the findings were that women are most attracted to men who are 6 years older than they are.