There really isn't a good way to tell. American beech could get that fat in as little as 80 years or so, or it could be much older. The bark of many tree species changes with age. So some sense of the age of the trees might be gained by looking at bark character. Beech, unfortunately. remains smooth its entire lifetime. Beech trees also tend to get hollow with age, so core data from them is limited. They have been documented to 366 based upon basic ring counts, but could potentially grow older. In the generally open area shown, I would not expect the trees to be of any great age. Sorry, just my opinion.
"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky