"Tata" and "mężczyzna" are clearly masculine because of their meaning, even if they sound feminine and have feminine declension.
Some other words that work like that but are a bit less logical are for example "turysta" (a tourist) and "artysta" (an artist). Their feminine versions are "turystka" and "artystka". There are not many such exceptions, don't worry.
Ok thanks - it is confusing when words are masculine in meaning - but in function are feminine or decline like feminine words. :)
For some time we rejected it because it's a different construction, then we started accepting such answers.
However, "Mój tata kupuje rower dla mnie" sounds kinda strange to me. This repetition of "mój"/"mnie". If anything, I'd say "Tata kupuje rower dla mnie"...
Also, emphasizing "dla mnie" could feel like "for me, not for you!"