Why would you need 64GB? If you are taking movies I can see the need for larger cards, but even then 64GB may be overkill as 30 minutes is the longest you can film at a time. One reason for using smaller cards is that all cards can fail. I will admit that I've never had one fail in 10 years, but imagine if a full 64GB was to fail. Disaster!
To answer your question, I think, but am not certain that the A550 can take up to 32GB SD/SDHC cards and the 32GB range depends on the make. 64GB cards are not supported according to Sony, but they only discuss cards that they make. So 64GB is inconclusive and in my opinion, inadvisable. A fast 16GB SanDisk card is what I would advise.
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS, FE 24-70CZ f4 OSS, LA-EA4 || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 f1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma 21-35 f3.5-4.2. || Tamron SP 24-135.