I solo hiked Whitney in July. Make sure you have a 2 or 3L water bladder and something to purify water. Pack more food than you might need. As others have said plenty of people on the trail starting at Midnight. Everyone you'll meet should be friendly and willing to help if needed.
Hiking Mt Whitney was the best hike of my life. I'll be back next year. I'd go back in August if I could.
