My observation is that the erj is/was a quick turbo prop conversion designed for a relatively short life span. At one point I recall a 20000 hour airframe limit. This has gone up as it has performed somewhat better and longer than designed. I don't think Embraer had two to three hour stage lengths in mind 12 years ago. That has saved a ton of cycles on the airframe. They still seem tired to me. The reliability of the older half of the fleet seems less to me. Twenty years for an airliner is a long time. Twenty years on a regional airliner is a very long time. Life limited parts, finishing parts, dispatch reliability all figure into operating costs. I dont claim to be an airline economist, but I surmise that at one point the cost of operating an older airframe crosses the line into a need to acquire new equipment due to pure economics. Eagle launched EMB 600 and 601 in May of 1998 in ORD, (I had a piece of cake and punch, there was some balloons too!) I believe both are back from TSA sabbatical putting them at 14 years this May. Time flies. I keep my opinion they are old. Albeit, some older then others.