We adopted our son at 9 months of age, pretty much the youngest age a child can be adopted in the UK, because even when it is known at the child's birth that, in all likelihood, it will be adopted, it usually takes that long to sort all the paperwork etc. We were incredibly lucky: we had gone through the lengthy pre-adoption appplication and then the Home Study process - it took about a year, and then a few days after going to Panel, we were placed with our son.
Why did we adopt? We had been trying to start a family, unsuccessfully, for some years. We had an absolute horror of going down the fertility treatment route. I had not wanted anything more invasive than Clomid and stopped when that didn't work. I don't think the social workers were 'suspicious' of that and seemed to accept it as the perfectly valid reason it was. The whole adoption process, with its intrusive and invasive procedures, was infinitely preferable to us. We are essentially very private and so found it all quite agonising, but gritted our teeth and stuck it out. With the most wonderful end result, which I view as a kind of metaphorical, truncated and very painful labour! Our son was meant to come to us and we were meant to be his parents.
The irony is that, a few years later, we desperately wanted to add to our family but had found dealing with Social Services so traumatising, even though their involvement in our life ceased once the adoption order had gone through. Going through all that again was too horrible to comtemplate ... so we faced the dreaded IVF. Perhaps because we already had our beautiful son we were able to deal with the treatment, which wasn't nearly so bad as I was expecting, and it worked, first time! Our second son was born and now I'm pregnant again with our third child. But we never, ever regret our initial route because it was what we had to go through to get DS1 and of course, he will know that he came to his family not as some sort of last resort but as a FIRST option.
I would say to anyone considering adoption - go for it. If you have the patience and stamina and can focus on what you want your end goal to be, then do it. Most adopters will tell you how difficult it is - and that is true - but once you are through the bureaucratic hurdles, it can happen smoothly and quickly, like it did for us. But, if you know that you could possibly conceive anyway, social services would probably want some kind of undertaking from you that you wouldn't get pregnant during selection and placement and for some time following, in order to make any adopted child top priority.