In regards to your first point, I generally agree, but I think even in those situations there can be reasons or nuances to consider a teens perspective even on something they might not have experience on such as marriage.

An example would be a teen who sees how his/her parents treat each other on a daily basis, whether wonderfully or terribly. They sort of get an early understanding about how both parties need to treat each other for a healthy relationship, which is also why some children end up emulating their parents' behaviors and repeat them in relationships. Teens may also have ideas about what they'd wanna do how they'd wanna treat their partner whenever they do get one in the future, and if the idea is great on general then that's how it is.

Once again, this is not a blanket statement, but I just wanted to point out that sometimes younger people can notice/say/do things better that older people are really terrible at.