Car seats - backwards facing until when

What car seat you use for your child? Rear facing or front facing?

We used Nuna backwards facing in US until he was 12 months but now traveling in Europe and purchased different brand (also backward facing) but seems like there is no more room for legs. He is 18 mos and seems uncomfortable.

It says you can keep backwards until 3 years (??) but how?? No space for legs? You fold legs and make child uncomfortable? I know it’s safer.. but how????

I fear to go somewhere in car as I know he is uncomfortable, and I don’t want to put him front facing. Help.