I think the progression from DE to SR makes alot of sense. The learnings carry over and it's precisely what I did. I agree that the learning curve for SR is much higher than a DE but it's also much more rewarding imo. With a DE, you learn a lot about angles, hair growth directions, skin stretching, making a good lather, how to use a brush. SR takes many of these skills to the next level but you build on it. I am still under the 100 shave mark with my SR but it also takes me longer to shave with a SR without a doubt - especially when you include the "maintenance time" of stropping, applying oil, etc.
If I was ready to teach my son how to shave (he is only 10) I will start him with a DE and then he can progress to a SR later if he chooses to.