No you're not too old or too single. However as you work full time, it would be difficult to take a child under school age. How do you manage in school holidays and taking and fetching your son to and from school. It maybe that he is collected by a friend or relative. The thing is with an adopted child, you would need to have adoptionleave to allow the child to settle and then have reliable arrangements for school holidays, child sickness etc.
The other thing is your own little boy. All children who are awaiting adoption are to a greater or lesser extent damaged by emotional, physical or sexual abuse, and the damage manifests itself in difficult behaviour, which could affect your own child. There needs to be a 2 or 3 year gap and the adopted child would need to the youngest so he/she wasn't competing with a younger child. That means you would be thinking of a 5 or 6 year old.
Contact your LA and ask to speak to the adoption team. They will send you further info and then come out and visit you. They will say if they think it not reasonable (one of the problems couldbe lack of space - the adopted child would have tobe a boy and how is your son going to feel about having to share his bedroom by a younger, possibly destructive child)but applicants are invitied to a preparation course and then are subjected to an comprehensive assessment and this is a 2 way process really, for you to decide whether this really is for you.
Sorry I am not trying to put you off - but am trying to give you things that sws may be wanting to discuss with you. But do get in touch and get the ball rolling - there is no committment at this stage, nor indeed untilyou have finished the prep course.
Give it a go and have a chat with the LA and take it from there.