Not defending pedophiles, but

you are about to defend pedophilia. rethink this and stop talking.

there was a time when 13 was considered adult.

and? Stallman is not talking about a previous time at any point here. also: that previous time was bad anyways. why would we want to--especially with respect to age of consent--go back to considering 13-year olds and younger to be adults? they cannot meaningfully consent to sexual relations with adults; it's just child abuse. all of this is why Stallman's words are abhorrent.

It’s still legal for teenagers to marry in most countries.

Stallman is not talking about teenagers. he explicitly distinguishes children (again, people <13 for him) from teenagers (people 13-17).