Tyler Cowen points to a new paper (gated) about characteristics in youth and correlation to entrepreneurial activity later in life. The abstract from Ingrid Schoon and Kathryn Duckworth:
Taking a longitudinal perspective, we tested a developmental–contextual model of entrepreneurship in a nationally representative sample. Following the lives of 6,116 young people in the 1970 British Birth Cohort from birth to age 34, we examined the role of socioeconomic background, parental role models, academic ability, social skills, and self-concepts as well as entrepreneurial intention expressed during adolescence as predictors of entrepreneurship by age 34. Entrepreneurship was defined by employment status (being self-employed and owning a business). For both men and women, becoming an entrepreneur was associated with social skills and entrepreneurial intentions expressed at age 16. In addition, we found gender-specific pathways. For men, becoming an entrepreneur was predicted by having a self-employed father; for women, it was predicted by their parents' socioeconomic resources. These findings point to conjoint influences of both social structure and individual agency in shaping occupational choice and implementation.
If you're further interested on this subject of characteristics of entrepreneurs, I recommend this paper by William Gartner; the literature review of studies should get you started.
Regarding this new Schoon and Duckworth paper, I can't comment on the specifics because I've not read the paper. But skimming the abstract, this feels like the right time to put some sunlight on an old, persistent problem. An old problem about youth.
I cannot emphasize enough that entrepreneurship occurs across all age groups.
This Kauffman Foundation Anatomy report series found the average and median age of entrepreneurs to be 40.
Education and Tech Entrepreneurship (Kauffman Foundation report):

Mean and median are 39.
Kauffman Firm Survey overview report (partial of Table 16):

Mean and median are 45.
Kauffman Index of Entrepreneurial Activity (based on self-employment data from the Census Bureau's Current Population Survey):

Panel Study of Entrepreneurial Dynamics II, data on nascent entrepreneurs (those who are interested and are taking steps to but have not yet formally started a business, so a bit of a leading indicator):

If your data cuts off at age 34, you are missing out on the majority of the entrepreneurial population. At any given age, you have a mix of entrepreneurs who really wanted to start a company and have wanted to do so for a long time and those who opportunistically became entrepreneurs/"I had no idea I would do this." My guess is that the younger age cohorts have a greater mix of the former and less so of the latter. Also, presumably at a younger age you are much more likely to be under the direct influence of your parents. I suspect both of these issues help explain the strong links between parents' characteristics and entrepreneurial activity that Schoon and Duckworth find. I would like to see this research updated when the data for up to age 40 are available, then age 50 (and so forth). My hypothesis is that the predictive power between early-life influences and adult-life entrepreneurship will diminish.