The human noble was Fergus' younger sister or brother and guarding the castle with him and your dad gone was to be their 1st big responsibility, so they must've been late teens (17-18) to early 20s (imo 23-4 at the most).
The mage was young because they only became an official mage (non-apprentice) during the origin, they could be as young as 15-16 or up to 23-4 like the HN imo, because you're described as a prodigy (fastest Harrowing ever, star pupil) so Irving would think you ready at a younger age than lesser apprentices.
The dalish elf was a hunter, implied to be reasonably experienced, so you could possibly be older but not too much since you're supposed to be around (or even the same) age as Tamlen, who looks in his 20s, so imo 22-23 to 28-29
The city elf is on their wedding day, so probably 18 to 20, though the marrying age is never stated
The dwarf commoner could be older since the sister is a younger one and she's of marrying age, so maybe 25. Could be a bit younger or a few years older. It's implied you're Leske's age and he could be in his 30s for all we know, but you probably don't have too much difference with your sister either, which is why 25 sounds probable to me.
The dwarf noble is the middle child of King Aeducan, so likely a few years older than Bhelen, who's an adult, so at least 23 I guess, could go higher but not too much because first, Trian doesn't look that old and second, because your father says you're the best warrior of the House but he's only just now giving you a unit to command
Hawke had to be at least 20 (or 19 if Malcolm and Leandra were crazy about having kids) since Carver and Bethany are twins and they're 18, but the Legacy told us Leandra was pregnant when she fled Kirkwall with Malcolm 25 years ago, so 24 or 25 depending on how far pregnant she was.
Bump all those by 11 years for Inquisition. Where they said 20 to 40 in a general sense but I think that doesn't apply for all of them. The non-mage humans are a younger sibling and their description says they're to be forced into the chantry or templars, not have been, they haven't started their career yet, so they must be pretty young, I'd guess around the Cousland Warden's starting age. And the Dalish Mage is still a First, though I suppose it's possible for one to be 40 the Firsts we've seen were young, in their 20s. The others have more leeway. Dalish Warrior or Rogue is a hunter, a very trusted (or most trusted) one since they're given the task to spy on such a big event, they could be any age where it's reasonable to be a hunter. Human Mage was part of a Circle when the war began, Circles have members of all ages. The dwarves are Carta members, same applies. And the Vashoth are mercs so same applies too