In the play's opening act, Othello relates how he and Desdemona began their relationship. Brabantio had invited Othello to his house and during those visits, Othello told stories
of most disastrous chances,
Of moving accidents by flood and field,
Of hair-breadth 'scapes i' th' imminent deadly breach,
Of being taken by the insolent foe
And sold to slavery; of my redemption thence
And portance in my travailous history
and other marvellous adventures. A young, motherless girl in charge of her father's household must have been impressed by this man who had lived such a risky, exciting life outside Venice. In addition to be physically different from "the wealthy, curled darlings" (I.ii.68) that made up her social circle, Othello is older than Desdemona and undoubtedly a father figure for her. It would not be unreasonable for her to feel the security she had with her father with this man. It is perhaps this comfort that allows Desdemona to declare her love for Othello because of "the dangers I had passed" (I.iii.167). Logically, an experienced general like Othello should have known better than to mistake hero worship for true love, but possibly because he had denied himself a meaningful and committed relationship to pursue his military career, he was more than susceptible to Desdemona's pure and sincere emotion.
The difference in their ages means that there are significant differences in their backgrounds. Desdemona's mother has died and is now a vague memory. As the daughter of a wealthy merchant, Desdemona would have had a very protected upbringing, and she would have been taught how to be a good and dutiful wife to a man of her father's choosing. Her father would have negotiated this marriage for her, and she would have been escorted to many feasts and banquets. In this sense, Desdemona has been prepared to handle the social occasions that Othello's position in Cyprus requires. It is an indication of Brabantio's lack of consideration of Othello as a marriage prospect that he allows Othello to spend so much time with Desdemona.
Her elopement, however, without her father's consent or consultation, underscores Desdemona's impetuosity and propensity to act without regard for the consequences wither to herself or those around her. This behavior does not correct itself after her marriage. In Cassio's suit she is relentless to the point of annoyance. On the other hand, Othello is a career soldier. He has worked hard and suffered much discomfort to reach the rank and status of general. In this leadership position, he is unaccustomed to challenges to his authority. Such a practice in the army would lead to chaos. As long as Desdemona sits adoringly at his feet and hangs on every word of his stories, offering tears as a compassionate reaction, Othello is not threatened. Her insistence to the Duke that she accompany Othello to Cyprus contradicts Othello's request that she be cared for...