Age reminds us that we play a game with physical boundaries. However there is always a way to push the limit and trick the game to get an unfair advantage.
The lower limit
What Nature says. In French we have a saying that goes like this “tant qu’il y a pelouse il y a match”. We can translate by “as long as there is grass ready, the football game can start”. I think you understand that grass refers to puberty signs on the girl’s body and the game refers to the intercourse. For nature, there is no precise limit except the physical limit itself. There is a lower and a upper limit on this aspect (which is quite obvious for women). However, humans struggle to control themselves so societies came up with laws.
What society says. 16 years, 18 years, or whatever. You can go to jail for a matter of days, hours, or seconds (what if you start and finish over two periods of time?). This is quite excessive but it is only necessary when you live in a world where people don’t love themselves.
What spirituality says. We are all one, we should love each other, without boundaries, blah blah. But actually they are really not sure because they usually run away for all material consideration.
What you say. You have many ideas. Good. However most of them are not yours, but the results of a propaganda started at an early age. It starts with your parents role models. Then, what they do or say to you, and what the society show what you should be like (and as soon as it becomes a norm, no one will dare trespassing the forbidden area). As a result, people forget that they can think by themselves (it easier to go to a restaurant than to cook by yourself indeed).
Age gap
The upper limit don’t need much words because we all agree that age gap is mostly in the same direction. If you are clueless, the answer is that the male is usually older.
Age difference seems a challenge, or maybe it is the opposite. This is just a tool that we can consider for a smart choice. Nature chooses by itself usually. If you put aside the social class, age number, assets, there will also be the physical and mental aspect to make a decision (as well as genetics and emotions but this is not something most people can be aware of).
The main difference between a good buddy and a girlfriend is usually that you can fuck the latter. Remember, the article’s title is “Including practical to spiritual thought” but the opposite works as well: including spiritual to practical life. This is the most obvious difference, not necessarly the most important. And that is also why and sexual orientation should not be discriminated. Sex is the cherry on the cake, but…

I think it is important to know where this age gap can be a problem and why it can be a problem. For example, it can be what other will think about it. Knowing ‘whys’, is important since you will be able to judge if it is relevant for your happiness or not. This 3D world will cease to exist at some point. We also meet souls when we meet each other. This is something we should remember: Not giving any fuck about what other people think.
Our generation is taught to be equal (always on an outside perspective, in fact they will never teach you that you should treat your emotions inside yourself equally) and they allow a certain gap but will judge you if you exceed the limit they accept. 15 years gap seems big. At the beginning. As time goes by it becomes less and less obvious. 60-75 years old people can also hang out together. I could have said 44-59 or 15-30 to manipulate you. The gap doesn’t change. Number represent something actual, but most of the time it is also a bullshit. African girls are mature earlier. Asians look like kids until their 30’s. There is not only a physical difference, but the difference about experience and the mental awarness (or IQ).
We are incarnated spiritual beings. Some can’t see the spiritual part, some others run away from the incarnated one. Some try to handle both sides. And in my opinion that is the only way out of this mess. Including practical to spiritual, and being more spiritual in every act will certainly make you feel better and subsequently make a better word.
With a minimum of a 15 years gap you will be ready to have a long run with best of both world (Remember how a girl is usually less attractive after 30 and a man has more finance and experience after 45). Age doesn’t mean anything but it is still a useful tool to make your life better.
Life is a scam, don’t fall for it.