I am no expert, so take this with a grain of salt. I think that if you cash flow $300 per month, you are doing quite well, AS LONG AS you have reason o believe that no major repairs will be needed in the short term. You asked about buying older properties and the biggest issues I have found is that roofs need to be replaced, HVAC needs servicing/replaced, and sometimes there are foundational issues (not super common). I you know how to swing a hammer or turn a wrench, you can save a ton of money on the maintenance side of things. If you are not super handy, I would suggest getting on YouTube to prepare yourself, or pass on older properties.
You did not specify the age of the property so it is purely speculation at this point. Often times older properties come with aluminum wiring or lead pipes. These items can make it expensive or difficult to get insurance for as well. Again, if you can do maintenance yourself, some of this may be fixable by yourself. A good electrician is going to cost a chunk of change to replace all of the wiring for the house, and a good Plummer will be pricey to replace the old pipes.
If the updating has taken place, then your repairs should be low and the $300 a month would be a great return for a noob in the investing realm. Just be sure to save that money up, and don't go using it for personal expenditures for the first 6-8 months and I would think you will have a great hold on your property.
If that roof is more than 20 years old though... I'd learn to swing a hammer to pass on the deal. Roofs get pricey quick if you don't know how to handle it yourself. I wish you the best of luck, and I hope this helped a little bit.