Jon Gray said he's never considered leaving Blackstone. Bloomberg/Getty Images Blackstone's president, Jon Gray, said bigger firms offer a lot of opportunity for growth. Gray said hiring, firing, and promotion decisions are key to a company's growth. Some have said young employees should opt for smaller companies, where they can maximize impact. Jonathan Gray , the president and COO of Blackstone, said large companies offer a key benefit to ambitious employees. Gray, the president and COO of Blackstone, said bigger employees give people more runway to rise the ranks, since there's not as clear a ceiling to growth. "One of the problems with smaller firms is, there's not a space. That smaller tree can't get sunlight," he said in an interview with Bloomberg that aired on Monday. Gray would know. He started at the firm at just 22 and said he was taken seriously from the start.…