What do you think the best age for a woman to begin building a family, with her first pregnancy?

I asked my wife for her opinion. We had our first when she was 25 and our second when she was 32. Both experiences were fine. We were able to be active in their lives and get them through college (with help from scholarships). Now we are still young enough to enjoy our grandchildren. Late 30's means you might be fairly old when and if grandchildren come along and you might not be able to enjoy them as much.