<human>: Condense the text into a few key points

I'm in retail. I'm a new assistant manager at a company that I love. I have a good salary, and even though I work long hours, I really do like my job. My store has three ASMs. Before me, no one was in my specialized position, so the SM had the two keyholders basically partner off on it. Now that I've taken over, they have a serious issue with me. 

Part of it, I know, is an age thing- the other three managers are mid to late 30s. I'm not inexperienced, however, and I do my job well. But when I'm closing a register, they'll step in front of me to "help". I was leading a meeting last week and they kept hushing me. And the other two ASMs have both had to cut them off when they trash talk me to associates. If I'm closing and say "I need you to _____", they'll either tell an associate to do it, tell me to do it, or just not do it at all. It's gotten bad enough that I locked myself in my office the other day to cry after one bitch ranted at me. This is my first management job and first full time job out of college and I'm not sure how to handle this. 

The other two ASMs have noticed and are seriously pissed about. But my manager is not super authoritative and, while aware of the issue, I'm not sure she's going to do anything. Both of these girls have been with the company twice as long as I have (6 as opposed to 3 months). I love my job, and I hate this bullshit. What can I do while waiting for my manager to talk to them in order to head this shit off?
<bot>: Keyholders at work keep undermining me (new assistant manager close to their age). It's my first management job and I don't know how to handle it.