There should be three components to the change over time:
- Change in the distribution of income (due to growth+inflation)
- Change in the conditional distribution of income (as the agent ages)
- Change in the agent's percentile (due to economic mobility)
The first could be extracted from the combination of total income growth (http://research.stlouisfed.org/fred2/categories/110) & income distribution (http://research.stlouisfed.org/fred2/categories/33001).
The second is difficult, as I have not been able to find a good source for age-conditional income distribution.
I don't want to endorse any specific study on economic mobility by linking here, as there are many muddled & conflicting conclusions. Intuitively, I would expect there to be greater mobility near the median than at either extreme.