They look healthy and sure look like they are growing well. I don't think they've started their new season growth yet, so that should start up soon. Where are you, by the way? Maybe Texas?

I'd give them about 3 more years and by that time you'll probably be writing in how to trim back ligustrums that are too tall!

Keep them trimmed lower down (uniform width) and they will likely keep trying to push new growth at the top.

Are they a specific cultivar of Ligustrum? Some are more dwarfing than others.