I am 63 and ride about 130 miles a week (road bike - Cannondale). With and increase in miles after retirement, I'm not sure about my seat height. I have a sometime sore right knee in front, below the knee, but I can't really count that because I was suppose to have a hip replacement about 8 years ago and I ride with my right leg cocked outward a bit because I can't bring it straight up.

My problem/concern is an inability to feel adequately sore in my thighs. I am 6', 195 and inseam of 33 3/4". My seat height is 29 7/8". Several years ago, riding much less, my thighs would get understandably sore and bulging with Lactic Acid. Now, with more training, even if I push a hard gear, I feel it in my outer, side of my thighs and in my hamstrings. If I lower my seat to where I know it is too low and to where my thighs are getting too much of the load, I still feel it in the side of the legs and hamstrings. If I push real hard to where my thighs should be burning, I still get the same side and hamstring fullness.

I am not in such great shape that I can't work hard enough to feel it in my thighs....I just have the feeling that somehow, I'm not getting the full use of the strongest muscles in my legs?

I am NOT out for speed records. I get my enjoyment from riding Centuries with my son and son in law!. I plug along, but still have to work hard on hills!

Thax for any thoughts.

I don't have nice cut calves like other cyclists I see, and no matter how hard I push or what position I am in, I do not feel any burning in them. This does not mean something is wrong, this means that this is how I am, and how I am put together.
Soreness in the front of the knee is typically indicative of too low a saddle height, but unless you get a proper fitting done, you won't know for sure.

This. But I'm puzzled by the hamstring problem which if anything, is usually indicative of too high a saddle position. It could also be that your saddle is too far back - try moving it forward slightly. And as far as hamstrings are concerned, stretch. Cycling does tend to shorten the hamstrings and it is always possible that as your quads have got stronger the relative strength of the different muscle groups has got imbalanced.

But in the end, you need to get advice from someone who can see you on the bike and knows what they're looking at.