-When is the best time to have children on the MD route?
Either before you start or after you finish! The universally worst times to have a young child are 3rd year of med school and 1st year of residency (so about midway through an approx 8-year training). Other than that, any time can be made to work, especially with a SAHD available. Just remember that once the baby is here, it will remain needy for quite a few years. (So eg 4th year of med school is generally chill, but then you have a still very needy 1 y/o in your first year of residency. However many women take a 'baby year' off after 3rd or 4th year, which can help with this problem.) If you are older, it's probably better to have them before med school or in years 1-2. If you are younger, it may be feasible to wait until later in your residency or after you finish.
- How old is too old to start a family?
I'd say that's a very individual decision. Depends on your fertility, your support system, and how many kids you want to have with what spacing between. Personally I think it's best to start having babies by 30 and finish by 35. Biologically, most people have reasonably good fertility until 35, and will still be able to get pregnant between 35 and 40. After 40 it's a big crapshoot. In general if you do happen to be someone who has a fertility issue, you have more breathing room to deal with the issue if you find it out earlier rather than later.
My personal concern is less with my biological fertility window, and more with the ages of my parents and in-laws, and how old I will be when the last child leaves the house.
-Do you regret your decision to be a doctor and a mother? Do you feel guilty?
Not at all, but I am in a very family-friendly fellowship position right now and I didn't have my first child until I was past the big training humps. Even still I had a fair number of hairy nights crying in call rooms with my first baby.
- General opinions about PA vs MD!!
Sorry I know nothing about being a PA, so haven't much to say on this one.