To become and remain the lover of another, who is older by several is a choice for the younger partner and an opportunity for the older partner..
Or it could be pure literature and poetry..like 'Lolita' - by Nabokov.
But 'Lolita is valid only for Nabokov..and none else..
Nothing binds them for long other than free, unconditioned assent and consent from both parties involved..
otherwise it is probably unhealthy and the incentives are of either the monetary or sexual nature..
No one says one should. have a younger lover.In fact it rather should be the exception and not the norm..
To begin with, such a relationship is a very strong illusory intoxicant and infatuation for the younger partner who is easily impressed and is suggestible to ideas and emotions..for the old one it depends..and is usually corruption.