Is age just a number?

Im dating my best friend he is 20 and im 25 (26 in may yikes!) and sometimes i feel like when i argue with him about anything or try to communicate openly with him he reacts like a teenager….but in other aspects of our relationship he is so deep and mature and centered….and old soul…..so im kinda caught in the middle of my own opinion on the matter….sometimes i just want to say “God your are soo young….one day you’ll understand what im trying to say.” but i have common sense…I am realistic i realize he is 20 and he has a lot of growing up to do and thats basically what your 20’s are about….learning about everything…and im a VERY VERY VERY patient person….and i really dont get frustrated easily but i see our disagreements going in circles and its because he is chosing to take what i say as criticism regardless of how i sugar coat it….or if im straight up blunt about it….but its like in 25 dude….im over the bullshit of drama and ive had the whole bickering and fighting over nothing relationships im over it….im not doing it again…and he came out of one of those right before we got together…now im thinking its habit…he gets defensive and chooses to shut down because its a defense mechanism…and he realizes this too he has confronted me about earlier in our relationship but its like starting up again…and its always when we havent gotten a lot of quality time together….so i totally get it…im just really wanting to be proactive about behavior that isnt necessary…ya know? How do i express myself knowing what i do about life and not make him feel like im a know it all and talking down to him… but also let me see he needs to be more mature in situations like those? Id really appreciate any insight because what we have in poetry and it is such a shame to waste one moment not being completely in happy in a situation that seems to have all the ingredients to make a beautiful and happy life together….
Peace and Love
Lotus