aries,
Although you’re right that it would be more fair and equitable to have the boys put money in escrow as well, the point here isn’t fairness, it’s solving a problem. The problem is the larger # of girls than boys, and the laws of “supply and demand”, unfortunately, are against the girls.
Your earlier point, if I understand it correctly, about the boys being less mature than the girls at the same age, is quite valid, and pba’s objection is misguided. Certainly, the argument can be made that it’s not a good idea for a 22 year old boy to marry a 22 year old girl because she’s been “around the block” more than he. Whether he’s to blame, or is simply acting “age appropriate”, is irrelevant. However this must be weighed against the age gap problem, and apparently, many great people who have agreed to the goal of closing the age gap feel that we can save the suffering of many bnos Yisroel without seriously compromising on sholom bayis.
I wish to disagree, however with your choice of terminology when you write “The system itself has kept these boys from growing and maturing”. Although there may be some degree of delay in the ability to handle responsibility in “mili d’alma” (worldly matters), the system is designed for, and for the most part is successful at, promoting growth and maturity in Torah and yiras shomayim.