Broadly he shouldn't be too concerned about his career now, mainly if he feels interested or not. Science is very broad, it could be that he hasn't really started into a part of science that he likes. For instance in TCD and UCD you may study natural sciences and specify your major in 3rd year. There's a huge range from molecular bio, chemistry, geology, maths, zoology, environmental... The science degree is a start, from that he can then choose to do the IT course if he so wants. I know many who have got solid careers from it although it may not be their dream career. People who I did science with ended up with PhDs, IT professionals, mining industry, chemical industry, clinical services, urban planning, enivornmental services, academics and so on...
If he's one of those that's really into programming on his home computer then go for IT now, if not it's no harm to wait.
Someone who likes science might also like medical related stuff (huge variety of courses out there, some can be done at master's level after bachelor's science but mostly no) if he is into more practical applications with people involved, medical related courses are usually very solid for earning and can bring you anywhere.
Between science, IT, engineering and med related they are good choices.