Welcome to the forum! It's heartwarming to see a new member do so many things correctly right off the bat. Those piggies are lucky to have found a caring new momma! I don't believe there's anyway to tell how old the pigs are once they're full grown. Just in case they are older in years, you may want to look at these pages on aging
Guinealynx's page and
the article by Vicki it links to. I hope you have many years with your new girlies though.