At the risk of starting a topic that could result in some controversial replies - here goes.
Firstly, I'm a male in my early 60's with an English wife and been fully retired here now around 4 years and while being far from expert on Thai culture I do see a lot of it and do understand and accept much of what I see.
Just yesterday I was at my favourite spa and was having a beer with the owners husband and a couple of members of staff when along came an ex worker who was heavily pregnant and was stopping off for a chat with her past workmates on her way to catch a bus into town and as I was going to same part of town offered her a lift and in due course off we set. Parked in the temple car park by the clock tower, I was going off to the IT centre above the old shopping mall and I believe she was off to the next door school to see a teacher about her son who is a pupil there. So, as we were walking out, just 2 friends walking and talking out of the entrance in come an elderly tourist couple and the woman on seeing an older man walking along with a very pregnant Thai girl had to make the comment quite loud enough for me to hear saying, poor girl - fancy having a baby with a man of that age. I simply burst out laughing not because it was nothing to do with me, but the womans assumption and the simple fact that it is also fairly common around Thailand anyway, with or without the pregnancy. I tried to explain to my Thai friend what I was laughing about but it was completely lost on her because although her husband is also Thai and around her age she happily accepts these common sights as simply normal.
So, to the point of my posting, what do many of the first time and even more frequent visitors to Thailand make of all these elderly men with women usually young enough to be their daughters, do you simply accept it and good luck to them, do you make comments like this woman did to me or simply accept it as part of local culture and none of your business or indeed any other point.