You'll be glad you came back!
I'm 50, 240#, a former MX, XC, and roadracer. I started back about 4 years ago, when I bought small XR's for my kids.
I'm on my second YZ125, ride almost all in the woods, and absolutely loving riding again. Being a former racer, I prefer to be able to ride a bike aggresively, so the 125's suit me to a 'T.' Heck, when I first started riding with adults, I became known as 'the fast guy on the XR100.'
I am still amazed at how much low-end a stock, but well jetted (critical!) '06 YZ125 has. If someone gets away from me it's because they are a better rider than me. I feel like the power of my current YZ125 is very comparable to my last 250, a 1981 YZ.
The ride and handling of a modern 125 will blow you away.
We are in America, though, where bigger is always better, according to most. The macho men will all tell you here that 'you must have at least a 250, especially a man of your size.'
I think that they are all trying to compensate for some other
inadequecy in their lives
I say buy whatever you think you will have the most fun on; I'm certain you'll be right.
Welcome back, KW