You can find statistics on gender in Tibia on a popular fansite here: https://guildstats.eu/census If you want to know about gender ratio in a specific world here's another link to the fansite: https://guildstats.eu/worlds please note these statistics only are based off a characters gender and not the gender on a players account.
I cannot find a fansite that has age statistics and I checked every fansite I could, not sure if this is provided to any fansite at the moment based on research. I know sometimes in the news Tibia will post statistics but it's been a while, here's an article I found about age dated in 2016: https://www.tibia.com/news/?subtopic=newsarchive&id=3720&fbegind=12&fbeginm=3&fbeginy=2001&fendd=11&fendm=4&fendy=2020&flist=11111111
"In 2015, the average Tibia player was born around 1990. This is still valid for today. So the average Tibia player in 2016 is around 26, one year older than last year."
..So going off of this article I would guesstimate an average age for the Tibia player must be around 30 now.
I also found an old poll which isn't very reliable because not a lot of players participate in polls and it's outdated but I'll share it here anyway:
"In the year 2005, we have already asked in a poll how old players were back then. Over 60 % of poll participants in 2005 said that they were between 15 and 19.
In our customer survey of 2011, there was also the question how old participants were. Over 60 % of participants of this survey then were between 16 and 21.
And then in 2012 a poll 29.84 % 19-21 years, 25.06 % were 22-24 years, 20.46 % were 16-18 years, 7.68 % were 25-27 years .."