If he really wants aerospace, then CSULB is the only choice out of these (with the assumption that waitlist = reject). Many people do go into aerospace from mechanical engineering, but UCSC does not offer that major either.
The other option is to start at a community college and prepare for transfer to a UC or CSU. Aerospace engineering is offered at the following California public universities: CPSLO, CPP, CSULB, UCD, UCI, UCLA, UCSD, SDSU, SJSU. Mechanical engineering is offered at a wider range of California public universities, including less difficult to get into ones like SFSU and UCM.