As for the ages here, the people most likely to migrate are the long term Reddit users that have had an account using third party apps since 2010 or so (because younger people have only ever known the official app). That self selects for anyone that was old enough to use Reddit in 2010 back when the user base was mostly high school / college / recent college grads. Someone in their late teens / early 20s back then will be in their 30s now.