They are not view as essential or nonessential. All are essential depending on the circumstances in life. Of the seven sacraments, three are sacraments of initiation, Baptism, First Holy Communion, and Confirmation, two are sacraments of vocation, Holy Matrimony & Holy Orders, and two are sacraments of healing, Reconciliation and Anointing of the Sick.
For cradle Catholics the natural progression is the three of initiation and Reconciliation. Generally this would be followed by marriage IF they are called to the vocation of marriage. For some they may be called to the vocation of the priesthood, then it would be Holy Orders rather than Holy Matrimony. Others are called to a vocation as Religious and would have neither sacrament but would take vows.
As an adult convert I received the sacraments of Reconciliation, Confirmation, and First Communion (I was baptized validly as an infant) at the Easter Vigil. I continue to receive the sacrament of Communion at every Mass and Reconciliation when I either need to go to confession or I have a mortal sin on my soul. The sacraments of Baptism and Confirmation are with me always, can’t be removed. I’ve received Anointing of Sick on a few occasions.
With the exception of Anointing of the Sick all the sacraments require a period of education regarding the nature of the sacrament. In the case of infant baptism, the parents are the ones educated. With that being said there isn’t a hard or fast rule saying each sacrament takes place at a certain age. It’s more about when a person is prepared for the sacrament.
Hopefully this helps.