It highly depends on what he wants to do in aviation and his motivations for working as a pilot. I can give my perspective as someone who had a full-time tech career and started the transition to working as a helicopter pilot several years ago. Some of this has already been stated in other comments - but thought I would add my opinions overall.

Signs you should not be a professional pilot:

* You're doing it for prestige. We're decades removed from the golden age of aviation. It may be cool to you to be a pilot - but most other folks don't view you as having a dreamy job. Don't be a pilot for how others view you, do it for you.

* You're doing it for the money. High paying(>$200k) jobs in airplanes are rare, and reserved almost only for captains at legacy carriers, and some corporate jet pilots. You need A LOT of experience and a lot of luck to get these jobs. And who knows how long these higher salaries will last. Some of the best paying($350k+) jobs in aviation are in cargo - UPS and Fedex - which are likely to be some of the first to automate away the pilot. Helicopter salaries are much much much worse. The highest pay I've ever seen was a heli-pilot with 35 years of experience and 30,000+ hours making $150k piloting a $22M aircraft. Given, he only works 6 months a year for that pay. But still a pretty terrible best-scenario pay rate.

* You're an adrenaline junkie who is looking for their next fix. If you want to get your license and go do crazy stunts out in the desert with no people around - be my guest. But you'll be eaten alive in most sectors of commercial aviation without a safety-first mindset. In some areas of aviation, sure, there's some risks. But they should always be calculated risks where the ends fully justify any added risk factor.

* You want to spend time at home. Most flying jobs are nomadic. It is hard on families, and isn't for those who are uncomfortable moving frequently and living the hotel life. Most pilots I know have been divorced several times if they've ever found someone who agree to be in a long term relationship with someone who moves so often and is around so little.

Signs you could consider being a professional pilot:

* You love flying, and nothing will keep you out of the cockpit. This is pretty much the only reason I think anyone should become a professional pilot right now. For many people there's something incredibly special about being in the air. As a hobby, aviation is incredibly expensive(doubly or triply so for helicopters than fixed-wing). So unless you have a career that can support your expensive aviation fix, you may actually be financially better-off flying for a living(as compared with a low/moderate salary job and flying away all your money). Finally, depending on what you want to do in aviation, there isn't always an equivalent option for hobbyist, and you have to go commercial to fly those missions.

Personally, I fall into the "I love flying" category. Even though my tech salary would have allowed me to fly small piston helicopters several times a week as a hobby, I wanted to challenge myself by flying more complex missions and aircraft than I could as a hobbyist - wildland firefighting and search+rescue specifically. This year is my first on a fire contract, and I can say without a doubt that for me the time/money/strain on relationships has absolutely been worth it. I love my job, and every day I'm off-site I wish I were working. However, there are some caveats. I'm single and enjoy being so. I seriously doubt I would stay in aviation if I found a long-term partner and/or started a family - the two do not seem compatible to me at all. Also, I still do contracting in tech for additional income. I know I have that as a fallback career if the aviation industry automates away the jobs I enjoy. So I'm not 100% sure if I would have done this without that fallback career plan.

With regards to automation in flying, I don't have a crystal ball. The FAA moves slowly. Very slowly. The only "fast" thing I've seen them do is add more regulations to UAV operators when they started becoming a potential danger to manned air-traffic. But I have never seen nor heard them being quick to loosen regulations or certify automation systems(in fact, FAA safety documentation discusses how automation can cause more harm than good when paired with a human operator - to highlight their thoughts on the matter).

But I would likely say that your brother will be able to find flying jobs for decades to come. Airlines will be slow to integrate fully automated cockpits due to regulation - and the first crash, I imagine, will likely roll back approvals for many years after(whenever it comes - we can't build perfect systems. And the NTSB would likely blame the system, even if pilots couldn't possibly have resolved the issues themselves). Also, if your brother is interested in any kind of back-country flying, I bet those will be even longer away from automation if they ever see it. Think flying people to rural airstrips in Alaska, flying float planes charters in the San Juans, or bringing supplies to villages in the middle of nowhere in Indonesia. The highly dynamic environments with unimproved strips and water landings would be a non-impossible but more difficult task than typical airports to automate. And the cheap labor available to these missions would likely not justify the additional expense of automation. Speaking of cheap labor - these back-country jobs pay absolutely garbage wages - but I personally know a couple former airline pilots who transitioned to rural flying missions because they were tired of flying a bus with autopilot and wanted to get back to what they considered "real flying".

Hope that mini-rant adds some valuable context for you!