2. You're still bitter about a past relationship.
If you still have a need to meet up at a bar with your mates and complain to your social support group about how "all men are jerks", "all women are alike", etc., you aren't ready to date again. If you're still feeling emotional pain, anger, anxiety, or depression after your break-up, you are too traumatized to come to dating with a clean, fresh perspective. Take a break, let yourself heal, and maybe even get some counseling. There'll be plenty of time to date when you can again present someone with a clear heart that is free of bias.
3. You're grieving a loss of your partner due to death.
This is a big one, but it's not as common as the other scenarios. If anything, when your life partner passes on, you're more likely to wait a little too long before you start looking again. In this case, since mourning is personal and different for everybody, only your therapist can tell you when you're balanced again.
4. You've been through many relationships in a short time.
How many is too many in how short a period? That's a question for you to decide. But, if you've been through ten relationships in five years and it seems like you spend half your life packing and unpacking things out of a moving van, this is probably a good sign to stop, live alone, and take a breath for a while. Some people have a problem with getting into a cycle, where they hop from one bad relationship to another. Especially people who have a history of abusive relationships have issues in this area.
Maybe you're obsessed with being with someone to the point where even a rotten relationship is better than being alone?
5. You have financial baggage.
Especially where children are concerned. Either you're stuck being a single parent or stuck paying child support. Even without kids, we all go through times of ups and downs in our finances. If you're one paycheck away from being out on the street and having more than five outfits of clothes would be a luxury, maybe it's time to get your financial life together before you look for somebody to share your space. This isn't as much of a hard limit as the other signs; even if you're temporarily broke, at least if you have a plan to get back on your feet again, most partners will understand. As long as your plan isn't "marry a millionaire"!