Flissiecat- some of it is how the sport is set up in this country. Having an "elite track" from age 8 means girls are selected very early for high hours and specialist training. They have to meet certain goals and get the required score at a competition every year to continue on elite track. It's very regimented with progression per year.
Anyone finding the sport later, even if they are very talented, will simply struggle to find a coach willing to take them on- by 8 even children will have advanced skills, and it's too much of a long shot to spend time trying to catch a newbie up. Catching up becomes harder the later you start.
It is technically possible to start later or join the elite track at 11, but again, non-elites tend to do lower hours and are coached differently, so in reality it's all but impossible.
I don't agree with it, and think we miss a lot of talented kids that are late bloomers/starters, but it is what it is.
BTW, personally I think a home beam is not a good idea. Expensive for one, and it isn't safe to do anything beyond basic steps. A line of parcel tape on the floor is cheaper, safer, and just as effective :)