What kind of old do you mean? What age is your tamagotchi?
And the 'flashing hearts' are probably because you've used the love potion/honey. But be careful - the love potion only lasts for a short period of time so if you don't want to waste it, make sure you only use it when you want to mate your tamagotchi with another tamagotchi of the opposite gender - when it's an adult aged at least 5 years old.