I don't feel age should matter. If you can have a 4-yr degree and 1000+ hours you should be able to go to a regional. You know going in you are going to be an FO for at least 2 years (age 23 min) and you have proven over the last 3 years that you are a driven person who puts priorities straight. Sure age can matter but many times a resume can show how someone is as a person. For someone to be under 21 and applying you MOST LIKELY graduated under 4 years in college and put flying as a top priority. It can definately be done. There are many people much older than 21 who act extremely immature. Age is only a number IMO.