If your son is above 14 years age before the CBSE Xth std. examination in which he is planning to appear, he is eligible. Please refer to the following link, where the issue has been discussed in details.
There is no minimum age - bar prescribed for class ten for the aspirants preparing for CBSE Board. However, it must be ensured that the aspirant must have passed class nine and the attendance before attempting class ten must be beyond 75 percent. As indicated by you regarding your son's age, he is fit for study in class ten and he can appear for class ten attached to CBSE Board in 2019.
As per CBSE guidelines if a candidate's age is more than 14 years he is eligible to appear in the 10th standard exam. So your son will be giving 10th in 2019 as he is now in 8th standard. When he will be giving his 10th he will be more than 14 years. So, he is eligible to sit for exam.
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