I think after the younger partner reaches age 30 the rule doesn’t matter anymore.

If a 30 year old decides to get together with an 80 year old then nobody should be shaming either of them. If they’re both mature, consenting adults then we should celebrate their happiness. Of course if one or the other is unable to consent by reason of cognitive disability then that’s a different story altogether (and would be a problem even if their ages were very close).