The only people that know which children our "ours" and which ones are adopted are family people out int he real world I dont tell unless i get this feeling and every time I have said something it turns out they have adopted or are in the process of getting ready to foster.
As far as the ages go
My Bios are18,14,13 and my Fc(soon to be adopted) are 8,3 1/2,2 1/2.2, and 10 months
I too have a had a harder time bonding with F but it is getting there.She has had some issues but theya re getting better she was just dx with adhd and we can start her on meds today!!
I have heard it said on here "fake it till you make it" and it does work.But with the older ones I think because they do remeber thier bparents it is harder.They feel like they are betraying the bparents if they have a good time with you are feel anything for you and in our case bparents were telling her and N that this was not thier home and we were not momma and daddy at every visit.Since the visits have been stopped she has gotten better even talking about if we adopted her what her NEW name could be!I was shocked but she has picked it out and wants to be called Rebecca Marie .
I suggest counseling for an older child if you feel any issues are there.The girls were in one foster home for 1 day with their sibs then another foster home for 6 months,then moved for another month,then moved in with us.Which I think has something to do with it as well(these moves were all in less than a year)
Just pray and take it case by case.