Can i play in lichess 45 45 at 13?

As per title. Also is there any other special junior leagues or something?

yes you can and for the leagues you should ask on a team

i am going to assume this is a hypothetical question, and i am going to assume it is about the lichess4545 league.
if the league moderators understood that a hypothetical account were to belong to a 13 year old person, they would not allow them into the league, because the minimum age is 16.
generally, and completely unrelated, i also recommend not telling people on the internet your age. especially when you are, let's say, younger than 20.

edit: unfortunately i do not know about any special junior leagues, but my understanding is that e.g. lichessladders has no age restriction like that.

edit 2: further i recommend you delete your forum post, as it could be construed to not be a hypothetical question. and as per my recommendation above, you should not tell people on the internet your age.

As long as you don’t tell them that you are 13.

You shouldn't speak about your age, because 13 is considered an unlucky number in many cultures.
P.S.: It's just a superstition, I was doing quite well at 13.