To answer this question properly is going to need a prospect double blinded controlled trial. That is not going to happen in a normal world.
You can try looking at historical data, like the one referred to in this Huff Post article but that type of restrospective data is highly flawed.
their average non-eunuch contemporaries, who tended to live ...
Tests that one may want to do annually:
Blood pressure; increased BP is a risk factor for heart disease
Checking your skin for moles, which can develop into cancer
Blood cholesterol and triglycerides (lipid profile); increased levels are risk factors for coronary heart disease
Blood glucose to check for diabetes mellitus
Dental check for caries