I think that there is like 60+ D1-D3 gymnastics schools out there, that is not many considering other sports. It is the top tier schools that recruit the really young and usually elite kids. If you (speaking generally from a gymnast perspective) are not a top tier gymnast, you need to look at that list and possibly focus on the lower half of those schools (if you are looking at earning a scholarship, if you want to just walk on then none of this really applies). Gymnasts, not parents, need to start contacting coaches from basically their freshman year of HS and it is like talking to a brick wall, but you keep talking.
A question that must be asked of the gymnast. What do they want? do they want to go to a big name school and be able to say that they go to such and such school, but might not compete OR do they want to go to a school that they will be able to contribute to the team immediately? Those are 2 important questions and the answer can help you decide which route you take through the process.
The reason you see freshman and sophomores committing is because of several reasons. A college coach can not contact a gymnast directly, but they can contact the club coach. They can come into a gym and look at anyone, but can not talk to them. A freshman or sophomore or anyone for that matter can go to a college summer camp and be seen by the college coach. A college coach can talk to them on "their island" (on their school property). A gymnast can call a college coach and if that coach picks up the phone, the college coach can talk to the gymnast for hours on end. This is how these kids are establishing these relationships with these coaches and doing what is allowed with the system.
There are several schools that do not recruit until later. As you can see on websites, that there are still Seniors committing, some with and some without scholarships. Quite a few schools are still recruiting Juniors too.