OK, well let's focus on things you could easily get data for, at a number of different levels.
At a race level, you easily can get age, sex and time by runner. You could do some interesting analysis on how winning times change with age, how average times change with age, or even how the variance or % difference in time between the winning and average times changes with age. You could also examine how the differences in times across the sexes change with age. Bear in mind that some of those relationships won't necessarily be linear, and others will show no relationship (which will be interesting in itself).
With a bit more work you could do some comparisons across races, to investigate things like how does the number of runners in a race impact winning time and average times, and what impact does climb, temperature, altitude or other environmental factors have on the winning time?
You could also get some datasets of elite runners, which would give you PBs, race history, year bests, weight and height. So you could analyse things like the impact of BMI on PB, the optimum age for a marathoner, the optimum number of marathons to run per year.
Finally, you could look at data across countries, and look at influences on national records at a given distance, such as population, GDP per head, average BMI, even temperature. This would be a good dataset to do multivariate analysis on if you're at that level.
Hope this helps.