Adam Bonica and Jacob Grumbach have written this article for the Journal of Public Economics. Here is the abstract:

Politicians in the United States rank among the oldest globally. This study examines how money in politics contributes to age inequality in political representation. Using record-linkage to construct a novel data set combining the ages of voters, donors, and candidates, we find that the median dollar in US elections comes from a 66-year-old — significantly older than the median voter, candidate, or elected official. Results from within-district and within-donor analyses confirm that age proximity with candidates increases contributions on the extensive and intensive margins. Finally, we simulate candidate fundraising by age under a hypothetical campaign finance voucher policy.