I see your new, so you might not know this but this topic really belongs in 'Help for New Tamagotchi Owners' or 'What Happened to My Tamagotchi!?" Thats ok though.
I've gotten oldies multiple times, and it's not that hard actually. Just continue to decline the matchmaker, and eventually your tamagotchi will change form into an oldie. Do NOT connect iwth the opposite gender if you have 4 hearts for them because of the risk of mating. To get an oldie, they cannot mate.