I always thought PhDs often get long in the tooth because research takes a long time and things can change drastically over that period of time, be it the resea

I always thought PhDs often get long in the tooth because research takes a long time and things can change drastically over that period of time, be it the research doesn't go the direction they expected or the world around them changed? If I was to go down the PhD path I'd consider it might end up taking quite a long time, because of exactly what you mention in your comment.