Everybody’s experience is different, but the key thing that should be present before you date is that you are truly DONE with your ex. It’s not fair to date someone if you would return to your ex if they came begging to have you back. That’s not fair to the person you’re dating.
Also, you need to have processed your breakup and done the work to grow from it and deal with your own demons.
That being said, this may look very different for different people. I started dating about three months after my husband of 24 years left. Normally that would be a TERRIBLE idea. But in my case, my husband had had an affair about 7 years prior. I had found this place and DB’d my husband, we had a successful reconciliation and I did considerable deep work on myself and my marriage. We had several very good years, but as he approached 50 and a midlife crisis, he finally left for good. That was really his third strike, as he’d also cheated on me at the start of our marriage. Once he filed for divorce, I was done. I had peace in my heart that I’d done everything possible to save my marriage, and I realized that after three strikes, there was no way I would ever be able to trust him again under any circumstances. So I was really completely ready to date, but it had been a 7 year long process of growth and letting go prior.