DA was always intended to be a series. That's why so much of DA is left open ended by DAO/DAA. Who is Flemeth? Eluvians? Where did the Darkspawn really come from?
Look at ME - in the trilogy it answers every question we had about the scenario provided (we know where the Reapers come from, why they do what they do, some of previous cycles attempts to stop them, how cerberus started, how the council got started, racial divides even between the 'older' races like Asari and Salarians. That game was intended to be a trilogy and they played the story in typical trilogy fashion, by the end of the 3rd all questions about the past were answered and only the future is left open ended.
DA was obviously meant to be a series as well. Before Origins was even done Gaider had plans for I believe 2 more games (high level ideas, not super specifics). Just because they were prepared for DAO to not do well enough to be continued doesn't mean they didn't want it (or have plans for it) to continue on.
Anyway: on Topic: I have no problems with DAOs origins having limited age ranges (the Human Noble is most obvious culprit as it is incredibly unlikely that the son/daughter of the 2nd/3rd most powerful family in Ferelden would be unmarried in his late 30s. He has heirs to produce after all (even if he himself is not the primary heir). Dalish I'd consider on similar ground because the low population of Dalish elves would put pressure on them to marry and make little elf babies, so a 40 year old Dalish Elf seems a bit of a stretch (but not impossible). Dwarves on the other hand are wide open. You see plenty of Dwarven Nobles that remain unmarried (since marriages are primarily political affairs and producing children can occur pre-marriage with no social stigma at all), so Dwarf noble is set to be anything. Commoner is a little bit more restricted but he could be anywhere too without too much hand-waving. City Elf you are in an arrangement marriage at the very beginning so it seems fairly set at anywhere from 18-35. Mage is wide open, as your pre-circle life never, ever comes up in the game you can basically be a hedge wizard who was caught be templars when he was 40 and still be perfectly fine.
Regardless I have no issues even if an Origin explicitly states a character is 25 years old. Age isn't a terribly important factor to my roleplaying experience, but ambiguous is always better in this instance as there are people who do care.