Ok how about what I have accomplished so far... my brother and I 23 and 24 years old. We bought our first rental house when we were 19 and 20 and now we own 7 rental units. I sell cars and my brother works on cars at local dealerships and we save all over our money to invest in businesses in hopes of being rich one day. We are up for any investment that can make us money and this seems like a good idea. Currently we have approximately $100,000 in cash and make around $180,000 cummulatively/year between our rentals and jobs.
Let me get my calculator. Umm, 23 and 24 minus 19 and 20, uh, ah 4 years! You and your brother have owned rental units for 4 years, you now own 7 units and you have $100,000 in cash saved up. Sounds good! I have never owned any rental units, but I have owned two houses, but not similtaniously. Both houses were built and purchased new. After some time both these homes required an infusion of cash for the replacement of appliances, water heater, roof, windows, paint, siding etc. A hundred grand in cash might seem like a pot of gold but spread over 7 rental units, I would assume of varying ages and upkeep, it ain't going to take you real far, provided you intend on maintaining your properties.
If the slum lord thing has been good for you guys, why not continue to invest in a business you are familar with?