What is the legitimate Islamic solution for a young man who wants to marry a divorced woman older than him, while his parents refuse because he is the eldest son, and due to the influence of societal opinions?

Online conversations must be قطع (cut off) immediately, and you must repent from them, as they are a door to temptation (fitna). The two who love each other are advised to marry, as the Prophet, peace and blessings be upon him, said: "There is nothing better for two who love each other than marriage." The Sharia does not prevent marriage to a divorced woman or an older woman. Try to convince your parents to marry her through rational people. If that is not possible, then you are obliged to obey them by not marrying her, unless you fear a greater harm. Patience and refraining from marrying her, out of dutifulness to your parents, may open many doors of goodness for you.