I have not been directly involved in hiring engineers (i have tangentially, writing up technical quizzes, chatting with them to get the cut of their jib, etc.), but I would say that the main source of ageism is the (probably often incorrect) assumption that the older someone is, the less willing they will be to adapt to new technologies, etc. If you show up to an interview and show a passion for the field and are familiar with a number of technologies, and express an interest to continue to learn, it shouldn't be an issue.
Also, if your friend was in their mid-fifties that would be a much bigger deterrent than being in ones mid-thirties. Our engineering team has a spread from myself at the low end (26) to probably mid- to late-forties on the high end, and the people in their forties weren't hired 20 years ago.
Honestly, the bigger barrier to overcome will be a lack of experience, and your friend's willingness to work their way up from the bottom. Assuming work or college experience started for this person around 18, they've been studying and/or working for 17-20 years or so. That probably means they've worked their way up in whatever field they are currently working in, and are compensated accordingly. Being willing to accept less money to get their foot in the door and work their way up/prove themselves is going to be a bigger deal, in my opinion, than just their age.
-Lee
