Why did Aladdin and Jasmine take so long to get married?

I think the celebration at the end of the first movie was their engagement or a second date in China where they visited during A Whole New World. That's the only explaination for the fireworks in the background. I know Disney is fantasy but I heard in Agrabah (India/Iraq) in the fan guessed era of setting (Don't ask me) fireworks wouldn't have been invented yet.

The fancy clothes suggests engagement to me.

As proof that their engaged Jasmine says in The Rat's Tail episode: "look I already told, I'm engaged to Aladdin." And in The Spice is Right episode; Aladdin has a minor freak out moment when The Sultan thinks the necklace Aladdin got Jasmine is a wedding present and sees it as a sign that Aladdin wants to start the wedding festival - to get married as soon as possible.

I think Aladdin had to mature first and get extensive experience and training to rule a kingdom and learn how to be a Prince as well as being himself. I don't believe you can marry into royalty straight away after living on the street. One would have to gain trust first. Trust instead of lying and stealing. At the end of the third movie he's knows exactly what he wants, he's not afraid of commitment anymore, evenually he'll become Sultan and he wants to be with Jasmine forever and ever.

He needed time to mature. And in the process got to know Jasmine, The Sultan and the kingdom.

Because of the dragon

Great question. Perhaps it was going under the premise that changing the laws for Aladdin and Jasmine to get married would take a while and couldn't happen overnight?

At the end of the first movie they are definitely just celebrating the engagement and I do think it is over the top but I also think the father was over the top happy to finally be able to rest assured that his daughter would in fact, get to inherit his kingdom.

There were two straight to video sequels made after Aladdin. In the first sequel Aladdin 2: Return of Jafar, Aladdin and Jasmine get in a small fight that delays the wedding as well as Jafar shows up again and they have to defeat him. In the last sequel Aladdin 3: Aladdin and the King of Thieves, the wedding is finally supposed to take place at the beginning of the movie but they are robbed by the 40 Thieves. Aladdin finds out that his father is alive and involved with the thieves and goes on a quest to find him with Jasmine's encouragement. This movie does end with them finally getting married.