@Sanz - jyeshthest was around 32 when Draupadi got married.
@Anu - I remember you already told me that. But his presence there is surprising. And Karna chose Arjuna because he was basically an archer & only Arjuna was the P side archeer equal to him. That also was according to battle rules, I think.
@ashne - Karna's no son accompanied him in Draupadi swayamvara. It is not there in KMG & CE. In KMG, Karna was a participant & in CE, he only accompanied Dury.
Arjuna had no problem in accepting Karna's duel challenge. But after rangabhoomi event, he did not get a chance. In KK war, he could not do it till day 15 as he was always kept away from Karna by Krishna till Karna lost Vasavi Shakti. On day 15, Drona got killed & Arjuna was behind vengeful Ashwathama & Narayana astra. On 16th day, when Karna took Vijaya (he used that bow only twice in his life AFAIK) & shot Bhargavastra, Arjuna told Krishna that it was impossible to stop Bhargavastra & Krishna takes Arjuna away making the excuse of visiting Yudhishthira who was in stress. The next day, they did a duel & Arjuna killed Karna, is what happened IIRC.