There are no rules in love. Lovers could experience one or two forms of love or all at the same time with one person or a different form for every person that we meet.
Some of us start off as friends experiencing "phileo" in the early part of a relationship but most commonly attraction between a boy and a girl happens first. The love that they experience initially is physical attraction -eros. This is often described as being "in love". It is the romantic stage when we see all the positive qualities in our partner such as the way he/she talks, what car one drives, and that one is smart & etc. This eros love is vital to commence a relationship and is natural. It strengthens the bonds of a budding relationship. We can prolong this stage, why not? In fact I think it will benefit the relationship if both go through a longer transition period from eros to phileo. Most of the time a relationship suffers when eros stage is cut short when a relationship transcends to phileo. In my opinion two people who are romantically in love should indulge themselves in this intimate attraction stage. They should be able to create enough foundation built from the time spent pleasing each other. But in order for a relationship to progress, love should then take a higher form -Phileo.
It takes time for 2 people to get to know each other and feel comfortable with each other. This is a long process and most of the time it is prolonged until marriage and continues on. When the flames of eros no longer shine, phileo takes its place. It is the love you discover through hard work, which is when Eros shows his most beautiful face, also known as phileo. Phileo is the love that keeps a couple together. Sometimes you hear someone say "our relationship is not getting anywhere". It means that the love is not taking a higher form. Either one or both partners are having difficulty expressing their feelings or uncovering themselves or deliberately avoiding further commitment to the relationship. Phileo or Philia is the "human love". It is the love we are all familiar with. it is a beneficial love in the sense that both will expect to benefit and requires that the love is reciprocated.
A couple, married or not, can experience eros and phileo simultaneously or at the same time or sporadically in a long-term relationship. The objective is to reach the ultimate form of love, agape. It is the sacrificing love that one gives without expecting anything in return. There is no age requirement to achieve this form of love. It is often done by choice of the giver and given whole heartedly. It is said that agape love is sufficient unto itself. When one gives agape love, one has the power to rise above the situation like when one chooses to act and show agape love to a spouse, it creates a loving atmosphere where eros and phileo can thrive in an otherwise mundane relationship. Additional problems can be prevented by responding out of agape and at the same time, the power works at nurturing the growth of the other forms of love.