My daughter is 3 months and teething also. We even took her to the pediatrician to make sure nothing else was wrong, her doctor agrees she is teething. But she also said it will most likely last for months because she's so young.
It's not too early, but it's earlier than usual. Remember that babies can teeth for months before their teeth actually come in.
Per my Dr there is no rule. It can happen anytime, usually it between 4 to 6 months, but it can be before or after.
My 2 month old baby girl is with her hands in her mounth all the time, but have not spotted any teeth yet!!