So assuming that 20-30 are at average incomes this means 6% of population is in that age range and making more than $100k. This is erring in benefit of your point … peak earning years are not until your 50’s.
There are several problems with assuming that this 6% has been saving and is ready to buy. What percent of this age group is married and wanting to buy? Overall, 50% of SD is married, I couldn’t find any marriage data by age but I would guess the percentage is much lower for 20-30 year olds (go to PB on the weekend). Anyhoo, assume 50% for lack of better data, now the contribution of HH in this age/income bracket who would be interested in buying is about 3% of the population.
Now the question is, how many of these people want to pay 300k for a small 2 bedroom apartment in UTC? Even with the conservative assumptions stated, I still don’t see much demand coming from that age group.