It is true that one CAN work even when collecting early retirement (not yet of normal retirement age) - and it is also true that when one is underage and started collecting first time in middle of year, often times that person may ALREADY have breached the 15720 limit. But, because much of that was earned prior to even collecting or being retired, to make it more do-able, they use a separate monthly earnings test for all months (and only those months) that he both collected SS in his first year AND worked. They prorate it, basically. He is still limited, certainly, in that first year, since he has asserted he is "retired", so one has to actually be mostly retired. In 2015, one had to be under 1310 in earnings, to be considered retired. So you need to look at each months earnings where he also got SS, and see if he earned over. Here is the link: https://www.ssa.gov/planners/retire/rule.html
OK, so he owes back 2014. Unless he finds they made an error, he will typically have to pay it back and waiver may not work (although never hurts to try). More likely to work is a payment plan - show them the hardship already you have to paying basic survival bills on the income available and ask for a payment plan. Rarely do they not provide that, if you prove your reasonable basic survival bills and show that they eat up all income. (Obviously, excessive non-survival bills won't help.)
Now, here is what I'd do prospectively - first, know that when he has to pay back because he really wasn't retired while collecting SS (early), it ends up INCREASING his later benefit because he no longer took early retirement (or all of it) for that particular month. But, if he intends to keep working despite not being old enough for retirement, the best option is often to tell SSA in advance what he intends to earn, so they will simply not send him the money he is not eligible for. Note that if he could avoid collecting any SS from 62 to 70, his SS benefit at 70 would be about 80% bigger than taking at 62! This can be very important if you already find that you can't live on an age 62 amount... you now have time to plan differently. It would have been better had he not already take at 62 (although is is less than 12 months, so technically, he could withdraw that application and pay back all - but it sounds like it has been spent and you can't afford to pay it back). But that said, and IF they send him payments even when he is working - consider banking those payments and not spending them (kind of how you lived on working income before he collected SS last hear) - that way when the SSA says you were over paid due to high earnings, you can pay them back immediately without stressing over it. Maybe even earn a little interest on that money.