yes, u do need to be an adult. if you find a partener you can turn the matchmaker down and connect your tamas when they are 6 (or 7 in some cases, mayb evn 8!) and they should get married.
You can have 4 hearts at teenage stage (that's usually how long it takes) but you cannot get married and have kids until you have been an adult for a couple hours. Just like haze said.