The risks of any test depends largely on how the test is being done. Fortunately, most diagnostic tests in modern medicine do not carry a very high risk of injury to our body.
As to whether the given risks to undergo a particular test is too high to accept will depend on a few factors. The most important factor is the reason to carry out the test and whether the result of such test is crucial. An example of a crucial test is getting tissue samples from an organ to confirm a cancer.
The next factor to consider is whether there is a reasonable treatment with a given test result. If there is no effective treatment available, it may not be meaningful to undergo the test however small the risk is since this will likely be an academic exercise with no effect whatsoever on the final outcome.
Another factor to consider is the accuracy of the test and the risk-benefit ratio. One may need to think harder if a test is not too accurate especially if it comes with considerable risks. On the other hand, another test with similar risks may be worth it if the result can benefit you tremendously such as saving your limb or your life.
In essence, age is not the only factor to consider for any test. In fact, we generally do not put too much weight on the age for most tests unless it is a special investigation which post a significant risk to that particular individual.
Dr Quan