you could probably keep that oscar in it for about 3 months til it's like 3-4".
then the fish will require around a 50 gallon.
then it could probably live in the 50 gallon til it's about 7" then which should be around 6-8 months.
you'd need to upgrade to around a 70-80 tank once it's around 10-12"
they usually slow down around 9" but still grow very quick.