I'm in similar situation: also a new ECE PhD graduate, working in my field of study, and also working on an exciting side project after hours, in a different fi

I'm in similar situation: also a new ECE PhD graduate, working in my field of study, and also working on an exciting side project after hours, in a different field. I'm 41, started PhD program at 35, long after I forgot almost everything I learned as an undergrad. I'm not sure I fully understand your worries though. What do you want your future in tech to be? What do you want to accomplish? The key is the drive to build something. Are you motivated enough to succeed? Is your hobby project exciting enough to keep you up at night (or would you rather be watching Netflix)? Regarding the sharpness - no, I don't feel any less sharp than when I was 20. I don't think the 20 yo version of me would be faster to solve hard research problems I'm struggling with currently, both at work or the side project. Sharpness is not a function of age, it's a function of your current state - physical (exercise, sleep, eat well), emotional (find the drive!), and mental (solve puzzles, read books, talk to smart people, try new things).