I'm not sure if this cat has the patience for real estate. I do like the idea of the fourplex. Do they even exist in CA?
I would use the money as down payments on single family rental properties. The properties I buy generate roughly 20-30% cash-on-cash return, but I do all the maintenance and management. 20% of $180k = $36k/yr income. It is not spectacular, but it's not a bad return. An entry level civil engineer in my area starts at $28-34k/yr, so it's not bad. Get a decent job to fill in the slow times and buy a new property every year. In 10 yrs, you sell off undesireable properties until you have 10 properties left. By this time, you have likely paid off most of the properties. Retire. This plan is not fancy. You won't impress chicks, but it sure as heck beats working for the man for 40 years. I do not miss the 20 mile commute in rush hour traffic.
Your friend has open doors many can only dream of having. However, your friend has age against him. How many of us exibited such maturity at that age? I sincerely wish him the best of luck.
Just a boring guy in Tennessee,
Jürgen