Ftm:There are actually 3 groups here that have to be analyzed separately: preteens, adolescents, and adults. The rules for each will be different. The hardest case is the adolescents. They shouldn't be conflated with adults, because we also have to be mindful of the incentives we are creating.
Here's the reality, though. ECNL is really in the scheme of things not that important. It's not academy ball like the boy's program highest tier. There's no drug testing so we aren't bending over backwards to ensure a level playing field. There's nothing to stop the same balance you propose as for a rec program: play up a year.
Here are the tests with adolescents:
-if you think testosterone is a performance enhancing drug that unbalances the playing field, are you trying to catch the cheaters? Presumably you are also o.k. with those that went on puberty blockers (or more drastically, transitioning) before 12/13/14 playing on the girls side without restrictions?
-if you think it's a genetics thing, are you o.k. with FTM playing in the girls league, even if they are taking testosterone, until they are ready to shift?
-if it's a safety thing, are you in favor of size/weight restrictions on all players, and not just those because of their status?
Because otherwise there may be something motivating the person beyond just concerns about performance, safety or genetics.
The answer for ftm is that ftm athletes on monitored hormone supplements have an unfair advantage. They should be welcome in a boys division.
Ftm athletes who are not on hormone supplements do not have an unfair advantage. They should be welcome in the division of their choice.
Ftm athletes who take unnecessarily large doses of hormone supplements are doping and should not be welcome in either division.
Hope that's clear.
Playing up:
Is a great solution for a pre pubescent girls league.
Playing up doesn't really do much for older girls leagues, because female puberty doesn't improve athletic performance. Take a look at track and field times. The boys are off like rockets from 13 to 18. The high school girls often still lose to 8th graders. The extra year isn't giving you as much.