Well, I agree they wouldn't have been able to take her head on, but if they had her sealed up it seems to me that they could have easily just blown up the whole thing or launched her into the sun or something rather than keep her in orbit? =P Could her powers really have prevented that from killing her? Doubtful, considering Edea could have been killed by a single bullet. But then why did they keep her there in the first place? Was Laguna perhaps vehemently against the death penalty?
I guess it boils down to the fact that her containment in space was primarily a plot necessity rather than something very well thought out. But if we just assume that they had a good reason for keeping her in orbit, then I agree, there is no real indication that the sealing prevents aging entirely. Well, the argument is still there that they perhaps put her in orbit and sealed her because they didn't want her to die because that might mean her powers being passed on, but we actually have no idea if that was why they did it in the first place, so doesn't amount to that strong an argument.
Hm, will have to put that in the next update of the Time/Ultimecia Plot FAQ over at GameFAQs. Will put your name in the credits Skyblade, if you don't mind (Big D's already there).