No you don't - have to apply now I mean. They just tell you that.
He can delay until next year when he may have a better idea of the kind of thing he wants to do.
But no, you can't do 2 btecs plus a technical and an A level - that's the equivalent if about 3 full time courses.
Your best bet is to go to at least 2 local colleges. Go and ask about BTECs in general, and then IT specifically. Ask both what they would suggest, if they can accommodate an AS (some can, we don't, but it depends on the college and its timetable).
A BTEC is a fulltime course. L3 Extended Diploma is the equivalent of A levels but may have slightly lower entry requirments. You would usually need Cs in maths, English and then maybe science or other course specific requirement.
L2 is the course you take to make up for low GCSEs in order to get on L3. You may not have English and maths at grade C. Sadly, with a D grade, next year your only option is to resit in 1 year - without all the support and time you get at school. Those with Es and below will still be able to take Functional Skills - and then GCSEs during their next course.
At level 3 you could be put on a Subsidiary course - usually to gain extra knowledge again to make up for low GCSEs. You may not have either English or maths and again, will be expected to retake GCSE. It would be possible, but not ideal, to have to take Functional Skills (having E or below in English or maths) and then GCSE when you go on to the Extended Diploma.
A levels require C in English and maths, plus whatever else they ask for. Funding means those 2 C grades are mandatory.
If you need more info let me know. As you may have guessed, this is my job, my specialist subject 