It's amazing how the conversation deteriorates and becomes a totally different topic of discussion.
Instructor old or young? Does age matter, what matters is the knowledge and the ability to teach it to others. Some great fighters suck at teaching and some great teachers suck at fighting.
Age doesn't really matter.
For the record, the mma gym next to my school recently hired a guy to teach muay thai who was younger than 30. I thought that was really dodgy...until I realized he was a professional fighter who had more than 150 fights in Thailand (being thai himself and growing up there) and probably have more experience in both training and coaching than everyone at my boxing gym put together :/
I would say if you're serious about opening up your own school, get experience teaching at your current school, if you're not doing so already. Also, learn more about the business side of it. It's a far different beast then I think some people would think. Not saying you're taking the idea blinded but felt it would be worth mentioning.
My first sensei in Shotokan started teaching at a local Boys and Girls Club for some time when he was a 2nd dan. Now he still teaches there and at his own location for the past 10 years.
My current teacher in ITF Taekwondo used to have his own school. Only because someone was willing to help him finance the place. He no longer has that location because he wanted to move elsewhere but teaches out of a local community center. He thought about opening up a new permanent location but did admit it would be a major commitment, not to mention the money in running a business.
I would say talk to other instructors, even in different styles and ask them for their opinions. I think you would get some interesting answers. Also if you do open up a place, don't do it above a restaurant. I know a few who have and their biggest complaint is the restaurant owners coming up stairs to complain about the noises. My BJJ school runs into that issue all the time. "Throw the person... lightly".
My current teacher
My instructor seems kind of old he has alot of gray hair. Besides age doesn't really matter just trust them to teach you if you don't then don't go.
Mmm, I guess I never posted on the age.
Experience is what counts, regardless of the actual age of the person. And that doesn't just mean years training. Just like Katriona I learn Muay Thai from a barely 30-something ex-fighter with over 200 fights under his belt (he's had a belt too, the Southern Thai Championship) and is a fantastic instructor who knows pretty much every trick in the book and seen it all.
I've also learned from two older gym owners, one an actual professor of fitness and Muay Thai and another older gent who used to fight. Both a great at teaching technique and strategy (but not the best model from proper technique themselves anymore).
So, umm.. no it doesn't matter so long as they are good.
The Muai Thai coach at my club is fat, bald and old but he produces pro fighters with solid fight records. As far as I know he doesn't hold any special record, he's just good at coaching and has a very solid grasp on the technical aspects of stand up fighting.