Unfortunately, by the time many people realize this, they have already done some things to set their credit score back.
It’s possible to rebuild your credit a bit more quickly with a few techniques.
The answer is that it could take a (long) while. How many years depends on what your current credit score is, and what steps you are taking to rebuild it.
Once you are authorized, your own credit score will benefit from their credit history (on that card). If you use the right card (like Citibank for example), they will report the main users limit and credit history of that card to your report.
Generally speaking, you can improve your credit by paying your debts down. If you want to rebuild your credit that much quicker, though, you need to pay the right debts down first.
Sounds a but counterintuitive, but as I just mentioned, one of the biggest factors of your credit score is the percentage of used credit vs available credit. The lower the percentage the better.