Ages on censuses are often very "iffy". I did, however, find a Gustava Forsberg emigrating from Liared, Älvsborg, Sweden (where a good possiblity for Fritz Forsberg/Fosberg came from), but the age of her emigration is not an age which fits the age on that 1900 census. Still, it is something to check out in Swedish parish records to see if there is any connection.
From the Emihamn database of CD Emigranten (the Emigrant CD):
First name: GUSTAVA Last name: FORSBERG Age: 33Gender: K (kvinna = woman) Parish: LIARED (where she was living when she decided to emigrate)County: P (Älvsborg) Port: GÖTEBORG Date: 1880 11 12 (Nov. 12; date of registering with the police to leave Sweden) Destination: CHICAGO Fellows: NEJ (Nej = no. She traveled alone on her ticket.) Source: 16:427:04056
I have found a lot of incorrect ages on censuses. We never know who provided that information and a lot of the women in my family were "creative" in reporting ages.