My opinion is it's never too late to start anything that's done effectively. It is a saturated market, so you might want to look into what could make your eBay store standout from the rest.
Read books about eBay stores and see what the 'norms' are and then start examining how you can break those norms without hurting your business. For example, if shipping is always five days, see what you can do to deliver your good in three days.
A good place to start is by reading eBay Income: How Anyone of Any Age, Location and/or Background Can Build a Highly Profitable Online Business with eBay by Cheryl L. Russell.
Lena West is the CEO and Chief Strategist of xynoMedia Technology, a New York-based firm that helps high-growth companies leverage the power of social media, blogs, podcasts and online communities.