I'm pretty familiar with Project 2025, but I don't recall that. The actual Project 2025 manifesto, 🤢 Mandate for Leadership 🤮 mentions marriage in a number of ways, including same-sex and even interracial marriage, but there's nothing in it about child marriage at all that I know of or can find, just a lot of self-righteous hyperbole about cis-het marriage and the family unit being the root of all good, blah blah blah.
I just checked it again to be sure, and yeah, marriage is not ever mentioned adjacent to anything regarding the age of the participants.
I'm not trying to challenge you, they're guilty of almost everything they've ever been accused of and far more that's even worse, but can you tell me where you got that from? Because if they're going to start this too I'd like to know more about it.