3 of the 4 FOs I worked with (a DAL regional) this month all had upcoming interviews at DAL. All 3 were on their 20s.

I know it's anecdotal, but I would guess the average age (from at least the regionals) is upper 20s. Of the 20 or so guys/girls I know personally that have been hired from where I work, I'd say 15 of the 20 were 20-something FOs. Just seems to be what Delta prefers right now.