Welcome to the forums and congratulations on the new addition!
I've seen budgies of all sizes and when fully feathered without markings as is the case with albinos, determining the age can be very challenging! With leg bands, there is typically a year indicated on them (the last two digits of the year anyway. For example "12" for 2012). If nothing looks like a year though, sometimes you can have the band traced to find out who the breeder was. The breeders here on our forums would be able to tell you more about that than I could though.
You'll have to post some pictures of your little sweety so we can see your feathered fluffball.