I raise a small flock of Dominiques and mine are very good layers. I get almost an egg a day from each of the Dom hens. I really think it probably depends on the strain or kind that you have. I got my Dominiques from a local breeder. Dom pullets should turn red in the face, comb and wattles before they start to lay. Mine will be 20 weeks a week from today and my pullet still has a pink comb.
You should check out the official Dominique thread for more information on the Dominique as well as the breed standard. I can't say enough good things about this breed- they are SUPER hardy, excellent foragers, very curious, docile, good dual-purpose birds....an all around great choice for the homestead flock. I think the Dom roosters are probably the most stunningly beautiful and graceful of all.