age is simply an average time when people can begin to develop said emotions. it's not mean to be a for sure rule to go by.
like i said before, its obvious that people dont realize what love is overnight. it happens over a long period of time, and i think that period of time begins near the end of one's teenage years or beginning of their twenties.
people without a certain degree of maturity can't feel 'actual' love, in my opinion. they only feel what they think is love.