I have a 14 year old son as well. I have no idea what time he gets up, because I am busy focusing on my job when I'm at work and not calling home to see if my perfectly capable teenager has chosen to get out of bed yet. There are days here and there when my kid has something scheduled in the late morning or early afternoon, or is getting picked up by his grandparents for an outing, etc. He's always been awake and dressed for these events. If he weren't, he'd either miss out or be embarrassed by someone coming into his room and seeing him dead asleep in his boxer briefs. Let him worry about the consequences of oversleeping - I'm sure your mom can handle it!
I think you need to focus on what you can easily control, which is his schedule when you're home. Make sure he's getting to bed at a reasonable hour (teenage bedtime in the summer is 10-11 in my house because I have to go to bed and get up for work). Don't go to bed before him, and don't let him bring electronics into his room. His phone, tablet, laptop, etc. charge in your room, and no TV or video games in his room. Move his personal electronics to a shared space like the kitchen in the morning if you don't want him going into your room to get his stuff. If he's in bed at 10 or 11, even a sleepy teenager will get up before noon. Pop in a say hi in the morning when you leave for work. It won't get him out of bed, and shouldn't, but it will prompt his internal clock that the day has begun and lessen the chance that he'll sleep the day away.
My guess is that he spends way too much time on electronics in his room at all hours of the night and then isn't getting a solid night's sleep when his body actually wants to sleep. Stop that now - it's a terrible habit for anyone to get into. If he wants to check his phone, he'll have to get out of bed and go to wherever it has been charging to check it. Same with any other electronics. Also, he's bored to death. School starts in a few weeks so that ship has sailed, but work with him this winter to figure out something productive for him to do next summer. State the facts - that when left to his own devices, he develops unhealthy habits and can't yet be trusted to maintain a reasonable schedule, so he'll need something structured for next summer.
Another thing that you can do right now is give him chores that he has to do every day. Leave a list of things that might take a hour. They have to be done before you get home and if not, you take his phone, personal electronics, game controllers, and change the wi-fi password for the following day. Then he does those chores plus new ones. If they're done by the time you get home, he gets everything back. If not, another day of boredom.
This isn't really about what time he gets up - it's about helping him get himself on a better, healthier schedule. He's bored, he probably has nothing to do on many days except watch YouTube videos, play Fortnite and text people. I totally get that as my son has had several weeks like that this summer. Fourteen is a tough age - too old for a lot of camps, too young for jobs (and they have to be driven to work anyway), etc. So there is going to be some wasted time. It's not the end of the world - come up with a better plan for next summer, and don't stress about this anymore.