A good summary consists of a few brief paragraphs summarizing your professional background, key areas of expertise, and any accomplishments you're particularly proud of.
Check to see if your mentee's profile gives you a good sense of who they are and what they can do for a potential employer.
To maximize readability, consider suggesting that he/she use a bulleted list to break up the text. (You can create a bullet by pressing and holding the Alt or Option key and typing the numbers 0, 1, 4, and 9. Or just use hyphens instead.)
Last but not least, the summary is a good place to account for gaps in their work history and prove how you've kept your skills fresh. If your mentee did any kind of freelance work, took a professional class, worked on a family business, or volunteered skills at a nonprofit, this could potentially be listed as work experience.