No easy answer. A woman with regular menses has a high likelihood of becoming pregnant within 6 cycles with regular unprotected vaginal intercourse. However, a number of other factors might need consideration to choose the appropriate time. General health, educational or work aspirations, finiancial stability and emotional readiness to settle down all should be considered. Take the time to assess your situation.
Depends. First you should take prenatal vitamins before pregnancy to decrease risk of birth defects, consider the expense of children, time required, and support needed to care for kids. If you have too much money, too much time, too good of a relationship, and you're ready to complicate it, early 20's is physically a good age for pregnancy.
No perfect age. When to try to get pregnant is a tough question to answer, and for every person that answer is different. Most people are physically able to get pregnant long before they are ready to care for a child. As people age fertility decreases, but I have patients having babies well into their 40's.