Some are fairly strict in what you wear, other's not.  Being you are older than the typical class, I would think there is some allowance to be self expressive; check with your instructor to make sure.

I wear split sole jazz shoes most of the time (believe it or not), socks or taped bare feet on occasion, and on a the same frequency as a "snowy day in the summer" ballet shoes.  I personally like the additional support Jazz shoes have and since I don't strictly do "ballet" it fits my image.

For the bottom half I Wear bike shorts (athletic compression shorts; variety of colors Red, Blue, Black, grey, green.  They allow you to move with freedom and as an added bonus wick the moisture away from your skin), and finally something to keep John and the twins under control (athletic supporter or similar).  

Top half a Shirt, either Long or short sleeve, or tank style shirt; typically whatever color stikes me.  The long sleeve is typically loose and I shed it after I warm up a bit.

Traditionally for men it is black tights, white T-shirt or Tank, and dance belt.  I don't do this.  Never had.  I wear what you would typically see guys wearing at a Gym as opposed to Ballet School.  To me the important part is you wear something that lets the instructor see your lines and it is something you are comfortable wearing; with all the new tight fitting athletic clothes on the market I cannot see tights being mandatory anymore (unless the instructor is a stickler).  

Yoga

I wear typically the same body clothes.  Yoga is done bare foot so you save a few bucks there, some people wear sweats or yoga pants; I would stay away from athletic shorts (the loose fitting ones) as they may on occasion expose a little more than anyone would want to see.  Yoga does require a "yoga" or "sticky" mat so your feet and hands stick in position.