Good news: children are actually listening to parents so keep saying what you believe.
Support him through GCSEs any way you can, especially English Lit and Lang which are really tough. At a minimum, if those are his last 'school' qualifications, he should work to make them as good as possible.
Take/send your DS to open evenings/days so that he can assess all the local colleges. Check out transport routes too - some colleges close to you may not acutally be very accessible via bus/train. In my area, there's no student transport discount for college!
Consider his A Level choices with him. What is he likely to study and which local college does best for that.
Reassure him that he CAN go to college. Financially, county ones are 'free' as long as he meets their entry requirements and you'll still receive Child Benefit.
If he doesn't have a job, try to help him find one. My DD worked shifts at the local on weekends. It was great socially and meant that she could pay for her own clothes and extras.
Consider what DS want to do for a career, would an apprenticeship be more helpful? Personally, I think apprenticeships will still be there for him if he has some good A levels under his belt and A levels will look great on a CV later.
Encourage him to think past A levels towards university or a further qualification. That might not fit his interests but let him know you utterly believe he can do it.