You can state the age group you are willing to foster.
We have a few families at church who foster and they usually have younger children.
Our first foster child was 13 and needed a good kick in the backside when we got him. Saw him a few years later and he was working and doing well.
Would not recommend this age group with small children in the house. Our DDs were 2 & 4 and it was a lot of work and they did miss out a bit due to his behaviour.
All the best as you make the decision to foster or not.