That means time with family in the Indianapolis area is over. He's set to head to Boston for his rookie season.
“I got kind of tired just sitting around the house,” he said. “I know my mom is probably ready for me to leave. She always says the house gets a little more messy when I'm around.
“I'm happy to get start a new chapter in my life.”
That chapter was on hold for about five months as owners and players couldn't agree on a deal. Now players and owners are set to approve it next week, with free agency and training camps to begin on Friday. That's when Johnson, a first-round pick, and his agent will be able to negotiate a contract.
The 6-10 Johnson spent the time working out in Indianapolis, Chicago and Boston.
“People were saying something might get done,” he said, “but I didn't want to get my hopes up too high. I'm glad they actually got it done.”
Johnson is set to join a Celtics team that includes standouts Paul Pierce and Kevin Garnett, plus former Boiler teammate E'Twaun Moore. The Celtics are one of 10 teams set to open league play on Christmas. They will play the New York Knicks in Madison Square Garden.
“I know I'll be really nervous,” he said. “It's like that in every stage, coming in fresh that first year. It's going to be tough.
“It will be my first Christmas I'll miss being at home, so that's going to be a huge adjustment. But I'm looking forward to everything.”
Johnson was at Mackey Arena on Tuesday night to watch Purdue beat Miami in the ACC-Big Ten Challenge. Johnson was honored for last year's All-America award by having a banner with his name and No. 25 on it hung at Mackey Arena.
Johnson finished with 1,919 career points to rank seventh in Purdue history. He averaged 20.5 points and 8.6 rebounds last season to win Big Ten player-of-the-year and defensive player-of-the-year honors. He joins Moore as the winningest players in school history. Both played in 107 victories.
Few expected this kind of success after Johnson arrived from Indianapolis Franklin Central. He was a reserve as a freshman before developing into a dominant player.
“It's a great story,” coach Matt Painter said. “He's a guy who worked hard to be in the position he's in. He's excited about the chance to play in the NBA. He was a guy who brought it every day. He came early and stayed late. He has some God-given ability, but he put a lot of time into his shooting and working on his game. He's very coachable.
“He's also very strong. A lot of people don't realize he can bench press 330 pounds because he doesn't look that way.
“It's special to see somebody develop like that and achieve some of his dreams. Now his career is just starting. That's what is exciting about him.”
Added Johnson: “To get this recognition for all the hard work you put in shows the university really cared. It's still kind of weird to me that my jersey is actually hanging up there. I mean, I just left. I always think it's for older people who come back to get their jersey retired. It's cool I can enjoy this while I'm young.”
Purdue will get its biggest test of the season when it plays at No. 12 Xavier today.