I recently interviewed Kimberly Palmer, author of “Generation Earn: The Young Professional’s Guide to Spending, Investing, and Giving Back.” Palmer recommends young professionals save at least 25 percent of their pretax income as they earn it. She adds that up-and-coming feds should take advantage of their retirement benefits, particularly the Thrift Savings Plan. I advocate the TSP as the best retirement investment vehicle available anywhere. Its low expenses, efficient design and simplicity make it better than any other defined contribution retirement plan I know of. I agree with Palmer’s advice to maximize your TSP contributions. Generally, I prefer to see…