Old and/or sick people should blame Avraham and Yaakov Avinu

The Gemara in Bava Metzia (87a) states that until Avraham there was no aging and until Yaakov there was no sickness. The gemara relates the following 2 stories:

1. When Yitzchak was born, the scoffers claimed that he was Avimelech's son. Therefore, a miracle occurred and Yitzchaks's face was made to look exactly like Avraham's. However, when Yizchak matured this caused problems. Since they looked exactly alike and there was no aging, people could not tell them apart. Therefore, Avraham davened for a solution and Hashem's answer was aging. The Medrash (בראשית רבה) is more explicit. It states that Avraham specifically asked Hashem for aging so that people would be able to tell him and Yitzchak apart.
2. Yaakov was old and wanted to bless his children before he died. However, he didn't know when he would die as there was no sickness. Again Yaakov asked for a solution and Hashem answered with sickness. פרקי דרבי אליעזר states this even more strongly (see גליון הש"ס ברכות נ"ג who quotes it) that until Yaakov no one ever got sick.

There are a number of questions that we can ask about this Gemara:

1. The world had existed for over 2000 years with no aging and people managed. It seems that Avraham had a problem because Yitzchak looked identical to him. How does that justify Avraham cursing all further generations with aging? Isn't that a bit selfish of Avraham?
2. The Torah states explicitly before the birth of Yitzchak that Avraham and Sara were old (זקנים). The story of Lot and the angels also mentions מנער ועד זקן, so it certainly seems that aging did exist before Avraham
3. The world had existed for over 2000 years with no sickness and people managed. Yaakov had a problem because he wated to bless his children before his death. How does that justify Yaakov cursing all further generations with sickness? Isn't that a bit selfish of Yaakov?
4. What does this say about Hashem's plan for the world? If Avraham hadn't asked would there have been no aging? If Yaakov hadn't asked would there be no sickness? 
5. From a biological/scientific point of view, no aging and no sickness is simply impossible. 
6. It is clear from the Rishonim and Acharonim (Maharsha, Mefarshim on עין יעקב)) that they understood this Gemara literally.