How many half marathon's is it safe to run in a 3 month period?

My brother is set to run a half marathon next weekend, one at the start of September then one in October. He is 32, fit enough to have run a half marathon before and continues to train. Is there any reason why running 3 half marathons so close together is bad for his health in any way? If not, are there any... show more My brother is set to run a half marathon next weekend, one at the start of September then one in October. He is 32, fit enough to have run a half marathon before and continues to train. Is there any reason why running 3 half marathons so close together is bad for his health in any way? If not, are there any training methods he should use in addition to normal half marathon training?
Thanks in advance for any help.
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