This is a fairly tricky subject. For starters - dates in Excel are actually numbers, in the background (the number of days since 1 Jan 1900. See How Dates Work in Excel - The Calendar System Explained + Video - Excel Campus
It's just that you can choose how to display them differently in Excel, as Feb-03 or 02-03 or 02/03 etc
If you have dates as data in columns, it's probably best to use
read_csv from the package
tidyverse. However, in your case, if you just want the dates to show up as column names, you could put quotation marks in your Excel file: "Feb-03", "Mar-03" etc. R will read that in as characters / words. Keep in mind that if you ever want to sort these names, R will not recognize them as dates and will sort them alphabetically.
PS I don't know exactly what kind of data you are working with, but if you need the dates to be recognizable as dates, you might want to re-format the data to have ID as column names, and have the date as a column.