Is it better to settle old debt or let them slowly fade away and just concetrate on keeping present debt current?

Your FICO score is made up more on how you pay your current debt than your old debt.

So make sure you keep up to date with the current stuff.

As for the old stuff…

Eventually they will most likely sue you for it before the SOL runs out.

If you can pay your old debt as well, you should pay it. Make sure you pay your current debt as well.

However, look at the interest rate you are paying on the old debt. If it is really high you might want to consider getting a lower interest rate for it.