Sure can! MC is 19 at the start of the flashbacks (Leaf End chapter), 20 when they join the White Fangs (Ilya: 20, Leon: 21, Saine: 15). 1 year until they get to Sienan, an additional 2 years until the execution, a year’s timeskip until MC is resurrected. So for the main story that puts our cast at ages:
As for the remaining ROs, whom you meet after the resurrection: Yu is 25, F is 20, and Eli is 27.
(So, um, if Saine being an RO squicks you out, F probably isn’t for you. :’) Saine not being an RO has more to do with (spoilers unless you did Saine’s option in the banquet) me wanting to have an aroace character as part of the core cast, than it does with the age gap.)