Aug 7th scan says 12 w 4 d. no lmp to go off. whats accuracy in telling me proper age of baby? and is that from conception?

Quite accurate: A prenatal dating scan at that part of the pregnancy is quite accurate. All dates are estimates, and in this case, conception would be about 2 weeks after the official start date. That means conception would be 10 weeks and 4 days ago, plus or minus one week. In general, the exact conception date is not important and is never known with certainty, with a "natural"pregnancy.