Not talking yet?

My son completed pretty much all of his milestones pretty early or right on time. He started sitting up at 4 months crawling and ulling to stand bith at 6 months cruising at 7 and took his first steps unassisted at 8 months and started full on walking by 9. He still isn't talking all he says is da da da da sometimes ma ma ma and he knows dad is dada. He used to say his name (not perfectly but if we said it he said it and you could still tell he was saying it.) But now absolutely nothing. When should I be concerned about it?