This question has many answers.
I think there are two types of men here - ones looking to settle down with a lady and ones just looking for sex every night with someone new - or a phoned in regular. The second usually turn into the first after a few years ! (OK maybe a 3rd who are not interested in women and just enjoy their own company)
If you are wanting to grow old with someone, you really need someone your own age or I'd say up to 15 years younger. (My wife is 14 years less than me). I know this lady will take care of me when I am old - there is a lot to be said for thai women 35-45. My wife still has the figure of a petite 30 year old, 45-48 Kg, etc, but has the mind of an adult and not a 12 year old brain in a 25 year old body.
If I just wanted sex then I'd be looking at early 20's to 30. Fit and firm. Those years were very enjoyable !
Simple question I would ask people in their 60's looking for a 25 year old is will she take care of you when you cannot walk, remember or even clean your own bum ! I see many young thai women with old men who just seem to be waiting for them to die to move in some thai husband now the house is paid for.
Lastly, I am forever worried that if their really is an afterlife that should my wife marry after my death , I could spend eternity on my own ! But if you can live with the thought of your partner being diddled by others for 60 years after your death, go for it.