From: Nicola Mody-Nikoloff mody-nikoloffn@axis-intermodal.co.nz
My guesses for the characters at the point we first see them:
Blake 35
Blake's clone gave his age as 34 in Weapon, and then confirms that he was 'born' just five hours previously, so it seems safe to assume that the real Blake was also 34 at that time. This would make Blake 33 or younger on first appearance.
Dayna 18
Told Avon she left Earth twenty years previously when she was just a baby. If she means Sarran years, and if Sarran years are slightly shorter than Earth years, then she might be this young. Or that 'twenty years' might be an approximate measure.
Tarrant 25
Was lieutenant on the previous kairopan harvest, which would have been 15 Earth years prior to the episode, as stated by Zen. Although this was his first command, he would not likely be any younger than 18, which would make him 32/33 on first appearance. Steven Pacey was somewhat younger than this, as he has mentioned in interviews.
No information is given for any of the others. Since Spacefall implies some measure of time dilation through faster-than-light travel, it might be that habitual spacefarers (such as Jenna and Tarrant in paticular) might be physically younger than their birth date indicates. If this is so, then such people would in fact have two ages - a biological age, and a chronological one.
As to Servalan, I usually reckon her much older than she appears, thanks to cosmetic surgery or some other rejuvenation technique, and place her at 50 minimum. But there is no canonical evidence for this.
The B7 Marvel Monthly gives Michael Keating as being born in 1947 (thus 30 on first appearance as Vila), with nothing equivalent cited for any other member of the cast. (It also notes that Glynis Barber was 'born in Africa' - shy of mentioning the 'South' bit in those apartheid-conscious days?)
Neil