Am open to the idea of slowly replacing them so I can get quality windows installed. 

Judging how the rents are $475/month, I'm also guessing this is either a C/D area or a very small town, which may contribute to higher tenant turnover, higher lease-up times, higher possibility of missed payments, evictions, etcRepairs at 5% also seems low, especially if I'm correct about the tenant quality/neighborhood this is in.

My guess is the quality, location, amenities are all worth the money.

I'm looking for ideas on how to attract and retain younger, quality tenants. 

It shouldn't stick out too much....drywall is pretty thin, relatively speaking.

Depending on your build quality you are going to start experiencing CapEx sooner rather than later since the property is already a decade old.Not trying to burst your bubble, @Nick Thomas, just trying to keep it real.

Generally speaking I try and find a good time for them, when they are in the area.

They will look good however there is a good chance they will get used and abused regardless of the cost or quality.

Click on a few of the ones with the rent value you think is reasonable and see what the interior quality of the homes are and compare whether your property would match that market.

I can see how it happens, you take a few wrong turns with your investment and you are not where you want to be, figurativley  and literally speaking.