You can do send a message if you have no other direct means to get in touch with this person.
If you have another means by which you can get in touch with this old high school classmate directly, it may be best to use those means.
For example, if you have a mutual friend who has their contact information, it would be best to contact them directly with this information.
Contacting this person directly will often have a better impact because you would be separating yourself from everyone else on the dating site.
It will also feel more personal.
However, if there is no real way that you know of to reach this person from your old high school class directly, then you can send them a message on a dating site.
If you choose to send them a message on a dating site, you should not do so within the context of how you used to communicate with this person back in your old high school class.
In other words, try not to call the person any nicknames that they may have had back then or reference something about them that you knew from your old high school class.
It could be something unique about their characteristics or the way they lived their life back then.
In essence, try to respect the fact that there has actually been a time gap.
A big mistake that people make when they send a message to someone from their past is that they think of that person as they were in the past.
Hence, they may say certain words or reference certain aspects of the person based on how that person was in the past.
The problem with this is that the person from their past may have changed.
They may no longer be the kind of person that they were in the past.
Some of those references may be completely opposite to who they are in present day.
They may not even want to be reminded of them.
Thereby, in opening a conversation by making strong reference to something about how this person was in the past, the conversation may be hurt from the very start.
Hence, if you choose to send a message to someone from your old high school class on a dating site, try not to make any reference to the past.
Instead, focus on the present.
After saying hello, try to learn about how the person is doing in present day.
It may be tempting for you to try to bring up a past occurrence from your old high school days with this person because you will feel the need to reconnect.
However, you truly have no idea what you could say that could trigger memories that the person doesn’t want to remember.
The last thing you want is to start your conversation with this person from your old high school class on a bad footing.
Hence, focus your attention on present day.
If this person feels the need to talk about the past, then they will bring that up.
Then and only then will you know that it is alright to talk about the past with this person.
You should really try your best not to get so excited about this person based on the memories that you have of them in your old high school class.
They could be someone totally different in present day.
The person that you remember as fun and spontaneous from your old high school class may be the opposite of that now.
They may be boring and predictable.
Hence, try not to allow your imagination to start running wild.
You may be looking at this person as a breath of fresh air because you are yet to meet someone of any true substance on a dating site.
However, you should not draw these conclusions so soon.
Give yourself some time to get reacquainted with this person from your old high school class.
Indeed, you may soon discover that they haven’t changed one bit.
However, try to avoid getting carried away with any expectation.
This way, you will be able to have a much more level-headed conversation with them and avoid saying anything that may turn them off.