Actually the love potion will work sometimes. It's just a item to use to make your tamagotchi mate faster. My v3 was 5 years old and mated with a v4 that was 3 years old. It just boost your chance of making love with another tamagotchi.
The love potion instantly makes the your tamagotchi and the tamagotchi you're connecting with have 4 hearts for each other in the friend list, but you have to be connecting with the same version, and your tamagotchi as well as the other tamagotchi must be an adult, and the one you're connecting with must be of the opposite gender.
The love potion does NOT make 2 tamagotchis mate, and it just makes them love each other instantly. The two tamas can be of different ages (as long as they're adults), but I don't think that it will allow an adult to mate with an oldie. Hope I was able to help!
i found that if U had 4 smiles with a tama, u would have a baby, quicker. my friend and i had a baby on the second time after useing the love potion! but before we used the love potion, we were 4 smiles, so i makes sence