Say your PhD is in Physics, I'm saying avoid going out with people who are also physicists at your uni or work in your building. Make friends with these people, of course! But keep it professional. I think it's really important to have that distance between your work and personal life. These are people you may work with for years or even your entire career!

However, I would really, really encourage you to get to know PhD students from other departments in your uni. There will be a mutual understanding of the PhD struggles. For example, my last girlfriend didn't really understand what a PhD was and couldn't really emphasise with me. She didn't get why I didn't have much time or money to do fun things. I think a lot of students have a love-hate relationship with their PhD work, which I've found can be really hard for outsiders to understand! I would try to go to uni events that are aimed at PhD students in general. For instance, I've just been to a seminar on thesis writing and met some nice folks from other departments. Just be patient and try going to different things and see what happens! :)

One other thing...I totally understand how this is a double-edged sword. On the one hand, it's obvious why dating a colleague can be a bad idea. But also, as a PhD student, the people you are most likely to have a lot in common will be other PhD students and academics! It is something that I am struggling with at the moment. Like the OP, I too see a cute girl in the corridor that I would really like to ask out for coffee. But again, not a good idea!

I totally feel your pain! The PhD has a way of wrapping its tentacles around your social life and crushing it until you are yearning for the hangovers of yesteryear. I too find not having anyone to talk to about my day or just chill with to be one of the hardest parts of doing the PhD as a single twenty-something. It's a lonely experience, but thankfully, it's also a relatively short one (3 years in my case).

I don't think pursuing relationships with other students in your institute is a particularly good idea. You pointed out that the other PhD students are too old for you, so you have some personal rule about finding a partner of an appropriate age. I would suggest a rule about dating people with connections to your career. It has the potential to end very badly!

Attend seminars and events for PhD students across multiple disciplines. Here you'll have the chance to speak to like-minded people in a similar situation to yourself. Good Luck :)

I had a really bad experience dating another student in my institute.

It started with that classic uni story...Boy meets girl on undergrad course. Boy and girl become good friends. Boy and girl start dating...

Three months later, the passion is gone. And by gone I mean dead and buried. The relationship became more about support and companionship. We became a witness to each other's achievements and a friendly ear for all of those student woes. However, we were supposed to be in a romantic relationship, and with this came all of the romantic expectations. We each tried to live up to these expectations, but it was forced and stressful and led to many arguments.

So why didn't we just end it and agree to be friends? This would have more the courageous and ideal option, but there is the fear of it ending badly. You become afraid that you will lose your valued companion and have to deal with the awkwardness and potential backlash for the remainder of the course. Your mutual friends would have to take sides and the whole situation would be horrible.

I wish I been brave enough to just pull the trigger and deal with the consequences. Instead, we struggled on to the bitter end of our degree (about 2 years), neither one of us truly acknowledging how bad things were getting until we finally broke up. We parted on good terms, but never spoke again.

Now that I am older and wiser, I realised how totally unfair the situation was for both of us. We deprived each other of the chance to form meaningful connections with other people and lied to each other for two years.

My point is, you can only have a meaningful relationship when both of you have no external incentive to be together, but choose to be anyway. Dating people that have some role in other areas of your life makes it less likely that you or your partner will be able to walk away.

My advice...don't date people from your own institute.