Scientists have examined for decades how maternal age affects baby health, but only recently have they started to investigate if the father’s age matters. Adding to the small but growing pile of data, researchers analyzed kids’ behaviors from early childhood through adolescence and found that the age of men at conception had a great effect on their child’s social skills.

The study, published in the May 2017 issue of the Journal of the American Academy of Child and Adolescent Psychiatry (JAACAP), looked at data from more than 15,000 sets of twins in the U.K., obtained from the Twins Early Development study (TEDs). The team focused on developmental patterns in social skills and noted differences in areas of hyperactivity, emotionality, as well as conduct and peer problems. Then, separately, they compared whether paternal age had more of an influence than genetic and environmental factors.

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Results showed that children born to fathers younger than 25 or older than 51 showed more prosocial behaviors in early development, but there was a ceiling. By the time they reached adolescence, these kids had fallen behind their peers with middle-aged dads. This was true across the board for social behaviors but not in any other domain, even after researchers controlled for maternal age. Further genetic analysis revealed that social development was primarily driven by genetic factors, rather than environmental ones. Notably, those genetic effects became more significant as paternal age increased.

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“Increased importance of genetic factors observed in the offspring of older, but not very young fathers, suggests that there could be different mechanisms behind the effects at these two extremes of paternal age,” Dr. Magdalena Janecka, lead author of the study, explained in a news release. “Although the resulting behavioral profiles in their offspring were similar, the causes could be vastly different.”

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Like many complex experiments, this raises more questions than it answers and more research needs to be done to duplicate results and determine biological correlations. Still, Dr. Janecka and her team hope that doing so will offer more insight into parental age and the potential risks associated with it, including but not limited to autism and schizophrenia, which past studies have explored. Until then, use the phrase “old man” with caution.