I work in Wales, so possibly different as the staying in education until 18 rule hasn't come in. But my advice to those looking for apprenticeships is usually:
Be proactive in looking and search frequently. Sone engineering firms advertise in the autumn for the following September and some employers may not advertise until the summer, so you need to keep checking on a range of websites. Many young people I work with lose interest in apprenticeships when they realise one isn't going to land on their lap and I dont have a nice menu to choose from.
Consider contacting local firms speculatively and ask if they would offer workshadowing / work experience as well, to show enthusiasm and gain more to out on CV.
Talk to local careers service or school careers adviser if there is one, as they may know of opportunities or at least can advise in where to look, CVs etc.
Consider a college application now as a back up because in my experience not many 16 year olds seem to get straight into apprenticeships unless they have contacts. He can always withdraw his application if he gets a job offer. A college course in construction welding, engineering could be very practical and different from school. And here most 'full time ' vocational courses are only 18 hours a week do it won't be college all day every day. This would give more relevant skills and experience to improve chance of getting an apprenticeship the following year if needed. One of the organisations that helps organise construction apprenticeships locally has said they prefer to recruit from college now.
In terms of English and maths, it depends on the employer / training provider used what they ask for around here, but I believe most apprenticeship specifications include functional skills / essential skills in numeracy and literacy for those who don't have the GCSEs. Generally engineering apprenticeships seem to ask for them though.
In Wales there is also the Jobs Growth Wales+ programme as a back up training course but I dont know if there is similar in England.