Well, my main problem was not the age gap, but the fact that IMO reincarnation does not work like it was shown here. It is not our task to find people from our past lives and to have the same relationship with them. It happens naturally that the souls meet and if someone was your lover in the past life, he can be now your brother or mother or child etc. So, it does not mean (s)he has to be your lover in his/her next life. I believe that if it happened like that, her task was not to have a relationship with him and to die with him to become a couple in next life again. They may be born as close relatives, for example. And also, if you had a certain disposition in your past life, it does not mean you will be the same this time. We have different tasks in different lives. It had a meaning that they were born this way and they should not have thought that they were "born wrong" and end their lives. I do not think that was the purpose why they were born. Also, I think that Pob saw Natcha as the man he loved in a female body, although she definitely felt like a girl, not like a transgender man. The screenwriter probably wanted to say that geneder does not matter at all but if it was like that, people would not have different sexual orientations and nobody would have the need to change his/her gender.
But I cried anyway and a lot. When you don't think about that too much and accept the screenwriter's way of thinking, you will most likely enjoy it. What I really liked was the acting (and directing) in this movie, it was exeptional. I felt like the actors actually were the characters they played.

Note: Sorry for my English, I'm not a native speaker.