An adult ADF should be no bigger than a quarter. Albinos - or ACF (African Clawed Frog) should NOT be kept in a tank with any fish we discuss in this forum! And they need lots of space and can live for over 20 years! ADF has a life span 3-5 yrs.
Check out this link - it'll tell everything you ever wnted to know and more:
http://www.allaboutfrogs.org/info/species/clawedordwarf.htmlADFs are SOOO cute! I still miss mine!

But, I am too sad to get more now.
I hope you can get some soon - just make sure the pet store does not sell you the wrond one because they often confuse the names, too!
PS - the picture you posted is an ADF! Can't tell it's age b/c there's nothing to judge size... but they will pretty much be full grown when you get them at a store - if you breed them, then you can see what they look like really young!