I do agree with you on the boy/man thing. I am the same as you over age although I wouldnt be able to compare a hairy bum with a boy's tummy in the way that you did. It took me fifty years to realise (and only then with help) that 'maturity' is not something that comes and stays: my own 'emotional age' fluctuates from day to day depending on who-knows-how-many external and internal factors such as what I'm doing, who I'm spending time with and how emotionally involved I am with them, how secure or uncertain I feel, how others are responding to me, whether I feel in control of my life or not, and whether I am hopeful about establishing a relationship or not.
As my 'emotional age' fluctuates so does my level of attraction to boy or man. At the moment, for example, after some time of forced seclusion due to illness, I am again much more attracted to boys - but this wasnt at all the case when I was working some months ago and therefore mixing much more with people . . .
I think our 'mind' or 'soul' tends to project into our sexual attraction the sense of 'what is possible'. In other words, as a mature person, I am more likely to be attracted to those with whom there is a fair chance of establishing a meaningful relationship. When I am ill, or feeling hopeless generally about the chance of ever doing that (ie establishing a meaningful relationship) then I am more likely to fall back into a purely aesthetic sexuality rather than a more rounded emotional response to the other person. By a 'rounded response' I mean that the relationship will be two-way and equal - which is not possible, say, with an 11 year old because he is not 'mature'.
That is my own experience anyway.