I am sure the person who told you that meant to say it will take a longer period of time before your Avos begin to fruit. Generally, when you nurse avo trees from seed without grafting them, it takes very long before they can start fruiting but if you graft them, it may take just about 3 years for your Avos to start fruiting.
The Avo trees will fruit even if you don't graft them but if you graft them from a fruit-bearing Avo, they will fruit in 3 years. Hope this helps.