Good Job Huy. When you ask a question: good idea to sell or should I keep it long term, you are bound to get all kinds of answers.
To clear up a few comments. 1031 can be a good idea but you have to identify property to exchange for and you must accomplish the exchange is a specific time period. Additionally, you CANNOT TAKE POSSESSION of MONIES transacted from the sell, you must use an intermediary until the 1031 is complete.
Now to your question Huy. It depends on your objective. If it is your goal to keep building cash to buy more properties maybe selling is the best course of action. However, even with that goal there are options to get cash out and still keep the property. However, if your goal is to create continuing source of predictable and sustainable cash flow for something like retirement planning or replacing job alternative then keeping the property as a rental would better meet those needs.
As for me, I am 61 and looking to retire soon so I am extremely focused on creating cash flow from multiple sources. BTW it doesn't matter the age, the earlier we start solving retirement cash flow the earlier we can either retire or do the things we want to .....its called Financial Freedom. It is hard to get risk free yield today. Real Estate is not risk free but when you are renting out at $1200 or below, those in needs are increasing thereby reducing your risk of finding a qualified renter. Lastly, you can always take a cash out refi on the money you personally put in the deal and keep moving down the road with none of your original money invested.
Don't look back, keep moving forward, and keep making good decisions!