The most important point here is that we do not use 'later,' in this way. Also - what you have written above is a statement, not a question. As a statement, the sentence should read "I am going to take my entrance exam in two years' time.." We use the construction "I am going to............." with plans in the future. You cannot use "later," because later is a comparative term - for example - he arrived five minutes later than he should have done. Or "He took the test two years later than he had planned to." So you have to use an expression of time that is not a comparative - in this case 'in two years' time."