I think the first time we were ever quizzed on career paths was in year 8/9, and even then, the choices made were trivial and with plenty of flexibility. For most, it was just about picking the right GCSEs to go on to do the right A-levels. In all honesty, GCSEs really don't affect career choices - It's during the A-levels when you really shape your future. For a lot of courses, you didn't even need the appropriate GCSE to do the A-level, so anyone doing GCSEs should just get a wide variety and find things they enjoy doing.
Are we pestered too early on to make career choices? Yes and no. In some countries, such as the USA, many people won't know which job they want to go into when they're at university and they will keep changing modules and majors/minors throughout. I'd say that's too late to be deciding.
In the UK, you can be asked quite early on, which is fine, but there's zero support or focus for students. We were asked to make posters describing our dream job and what we want to go into, but the teachers never asked the students if those were smart choices. It was more a case of "You want to become an astronaut? Okay, that's great! You do that!", rather than "You do realise that this is probably not going to happen, right?". No research into job availability nor stability of that industry is ever asked and the students are cuddled because the teachers don't want to crush their dreams. From the poster I did years ago, I've gone through 4 jobs and 4 changes in career focus because the work I wanted was no longer available or I ceased to become a suitable candidate. If the schools are going to ask about careers, they need to provide some decent information to the students about reality and second, third, fourth and fifth choices in life.