【Premature】 , 【untimely】 ,  【forward】 ,  【advanced】 ,  【precocious】  are comparable though rarely interchangeable when they mean unduly early in coming, happening, or developing.

【Premature】 applies usually to something which takes place before its due or proper time or comes into existence before it is fully grown or developed or ready for presentation or to actions or persons that manifest overhaste or impatience.

【Untimely】  usually means little more than unseasonable but when it is applied to something which comes or occurs in advance of its due or proper time, it approaches very close to  【premature】 in meaning; the term, however, applies not so often to what begins a life or outward existence before its proper time as to what ends or destroys a life, a season, or a growing or developing thing before it has run its normal, natural, or allotted course.

【Forward】 applies chiefly to young living things or to growing crops, but also sometimes to seasons, that show signs of progress beyond those that are normal or usual for things of its kind at the time in question.

【Advanced】  tends to supplant  【forward】 when by comparison with other persons, other growing things, or other seasons of the same kind or class the one so described is notably ahead of the others.

【Precocious】 basically implies an exceptional earliness in development (as in the germinating of seeds, the flowering of plants, the occurring of a process, or espescially in the maturing of the mind).

The term is also applied to qualities, conditions, or circumstances which properly belong to maturity but come or belong to one who is otherwise immature.