I think it depends on a number of factors, you, the child, the job and your finances.
My son was nearly 8 when he came home, 9 years ago today. He had a number of already identified and diagnosed conditions including ASD and was attending special school. Whilst I know many children much more severely impacted than him, he has certainly presented me with many challenges.
I initialy went back three days a week, so 0.6 fte. There were times in the last 9 years I could have increased my hours, others when I could barely manage the hours I did and only managed to stay in work was because I was part time.
My long term plan was to increase hours to 30 after GCSEs, in the event I went up to 4 days at the start of year 11, so Sept 2019, and it has been a struggle.
I should add I have been very lucky financially. We received an adoption allowance and he qualified for DLA which meant I qualified for tax credits so it was financially possible. I also have a very understanding employer and for the most part supportive line managers. I was signed off sick once for a month, which co incided with my least supportive line manager.
My son is now 16, has done very well and is reasonably independent. He still needs a lot of support and emotional propping up, I’m 56 and planning my retirement, I may go back full time for the last couple of years to boost my pension if I have to, but I will do compressed hours as its very useful to have a free day when the children arent around.
Don’t assume adopting an older child makes it easier. The school day is really quite short, you still have 13 weeks school holidays to cover. In the first few years the only way I managed the holidays was because I was already home 2 days a week.
You may have many more school meetings/ reviews to manage. I found having two clear days I could usually manage to fit most of my appointments in then without impacting on the days I was in work.
The short answer is yes, its possible to do full time but you probably won’t know until your child is home.
The last thing I would say is that I feel many adopters neglect themselves. Having time without the children around gives space for some downtime for you. Its not been without financial implications but for me the right balance has been part time. Also helps that I’m not in the least career focused, for me work is a means to an end, not my priority in life